I wrote the guide after finishing the game, not while playing it, so it seems I made some mistakes.
For those who followed the guide step by step in the earlier days, I am sorry about this.

Ver. 1.075b edit.
Made the guide neater & shorter by shrinking & combining screenshots.

I am assuming you have cleared the game at least once on your pace and difficulty of choosing, this includes you having cleared both the main game and post game.

This is important for familiarity; there won't be much fun in a metroidvania if I detail every single thing you have to do, so it'll be mostly minimalistic tips, but on some occasions I will not hold back on spoilers.

Start of game --------------------------------------------------------> Prologue: Bunny Meets Fairy
Reaching Rabi Ribi Town for the first time ----------------> Chapter 1: Adventure Begins
1st trip through Stele with 2 people found ----------------> Chapter 2: A Little Peek
2nd trip with 4 people --------------------------------------------> Chapter 3: Bunny in the City !
Finding 6 people --------------------------------> Side Chapter: Trouble in Rabi Ribi Town !
3rd trip with 6 people --------------------------> Chapter 4: The Mysterious Bunny
4th trip with 10 people ------------------------> Chapter 5: Back to the Beginning (end of Main Game)

Go to Hall of Memories + Forgotten Cave II -------------> Chapter 6: Beneath The Island
Go to Systemic Core -Red Area- ---------------------------> Chapter 7: Connecting The Two
Find 22 / 24 people (or 23) then go to library------------> Chapter 8: Irisu In Wonderland. (endgame)

Challenge rematch with the Prologue Bosses (Cocoa, Ribbon, Ashuri)

If my Steam hours aren't enough to convince you, here's my ingame experience tally.

============================================================================

There will be a lot of pictures after this, if you think they are too small,
just click on them and Steam should zoom the picture.

If the zoomed picture is still too small, click on the URL that you see in zoom mode,
this leads to a 2nd zoom that will display the original size of the picture.

as they will be your most mobility enhancing skill for 0% Item Run,
and quite helpful to sequence break in Speedrun.

You may have seen this picture in the Hidden Tech guide;

However, I was the one who made the picture using Microsoft Paint.

=========================================================================

https://youtu.be/gI9_gShAnK4
You might as well practice the other hidden techs that are natural to Erina without items;
slow movement + dash drop.
Doing those moves should net you some acheivements.

There are actually 6 Hidden Techs, but I'll leave that for the Hidden Tech guide. The ones you haven't done yet require items to pull off.

These hidden paths in the Starting Forest will start you on your 0% item run,
and should be your first practical usage of Reverse Wall Jump + Wall Kick skills.

Discovery courtesy of Steam user LeChatMG

"Cocoa skip, first hidden passage" ----------------------- "Cocoa skip, second hidden passage"

Another Steam player has kindly uploaded a video on this.
https://youtu.be/EsZVnXc83VI

If you attempt this, the following acheivements are also possible in the same run.

• Never picking up Piko Hammer
  
• Defeat Ribbon before meeting Cocoa
  
• Because this game is non-linear
  (Lilith acheivement)
  
• Never collecting health potions
  
• Never helping out Ribbon's friends.
  
• Leave everything to Ribbon.
  
• Fight Seana without the Water Orb.
  
• Senpai Noticed (Fight Saya as Rita)
  
• Senpai's Super Combo attack (Only triggers in Side Chapter)
  
• Running away from home acheivement

============================================================================

My recommendation: Because of your low HP and low offensive power,
SAVE OFTEN + CASUAL DIFFICULTY

The only you things you can have in Main Game that doesn't increase item % are:
- the Bunny Amulet, and the Rumi Cake + Rumi Donut, all given to you by Rumi.
- purchased buffs by people in Rabi-Ribi Town.
- Cocoa Bombs by Cocoa in Rabi-Ribi Town.
- Rumi Cake + Rumi Donut for sale by Cocoa in Item Shop, only during Chapter 6

*There is a separate guide noting these buffs, feel free to check.
https://steamproxy.net/sharedfiles/filedetails/?id=619973424

The methods I'm sending you below are meant to be a simple, try to do the important plot-moving stuff in one area before heading to the next nearest one; instead of zig-zagging all over the place more times than necessary.

001) You're in the Starting Forest.
DO NOT GO TO COCOA, head for Ribbon through the hidden path mentioned earlier.

002) Battle and get Ribbon as your partner.

============================================================================

003) Go to Rabi-Ribi town for the first time and see Rumi. (through beach and ravine)
Register Rabi-Ribi Beach teleporter in your map system before you go to town.
Also battle Ashuri along the way, IGNORE THE SUNNY BEAM ITEM.

004) NEVER GO INTO THE SHOP AND TALK TO MIRIAM. (She forces an item on you)

005) Go to Rabi-Ribi Park, battle Kotri with green powers.

006) Continue and make sure the Rabi-Ribi Park teleporter registers on your map system.
Instead of leaving the area by going left towards Azure Snow Land and Rita boss, head right of the teleporter and further explore Rabi-Ribi Park upwards.

007) IGNORE THE REQUEST FOR RABI SLIPPERS.

008) Head all the way upwards to Sky-High Bridge area.

009) Register Sky-High Bridge teleporter and since its on the way, you can do non-linear Lilith's acheivement first; but this requires you to avoid the Vanilla battle. Save your game first in the Sky-High Bridge area and see section on non-linear Lilith.

010) Continue past Vanilla's room into Floating Graveyard area and register the teleporter there.

011) In Floating Graveyard, battle Kotri with blue powers.

012) Continue to Sky Island Town for the non-linear Lilith acheivment (see related section).
After the 1st Lilith battle, head back to Floating Graveyard area, then head back into Sky-High Bridge area and battle Vanilla. You will be returning through the Floating Graveyard teleporter to go for Lilith again later in 0% Post Game; which is after you battle / recruit Cicini.

013) Warp to Rabi-Ribi Beach.
Head into the pyramid and look for for a hidden entry, you can drop down there with 0% items..
============================================================================

014) Find and batte Pandora. https://youtu.be/24dbCxrQTaQ
015) Go to Golden Pyramid's Teleporter and warp back to the beach.

016) Go to Volcanic Cavern's area through Rabi-Ribi Beach.

(Drop into the first pit you see as you head towards Rabi-Ribi town)

The following area is probably the hardest for a 0% Item run,
because you have to move quickly and it relies heavily on luck, but it can be done..

You have to rely on 2 possible enemies to bomb open that path.

017) Battle Kotri with red powers.
018) Continue onwards and use Volcanic Cavern's teleporter,warp to Starting Forest.
Proceed until you are almost close to Cocoa's area (the spring),
then head in and battle Cocoa. She is not recruited yet.
(This is an important trigger for 2nd Cocoa battle in the Forgotten Cave area)

Image shows how to exit without Carrot Bomb.

Now head for Golden Riverbank area

The outcrop that might seem too high to jump over can actually be broken to form a ledge.
Just follow what you did earlier, Ribbon attack.
============================================================================
019) Proceed through Golden Riverbank; ignore the lower path, head upwards and battle Ashuri again.

020) Head to Evernight Peak, battle Saya and then search for her.
021) After recruiting Saya, head downwards from the area and go to Northern Tundra Area.

Teleporter for Everest Peak area cannot be reached without the Carrot bomb and sliding ability.
============================================================================
022) Battle Nieve at Aurora Palace.


============================================================================
023) Ignore the Water Orb in the room behind Nieve; backtrack toward the path near the Save Point you saw earlier and drop off.

You don't suffer fall damage.

============================================================================
024) Move one room to the left towards the save point, this will trigger a cutscene with Nieve, and effectively enables you to meet Nixie at Icy Summit area.

If you went to Icy Summit area first without visiting Aurora Palace., you will never meet Nixie.

Right now there is an optional area on the lower path since you are close by and are on 0% item track..

- Not a recommended attempt if you are going for speedrun acheivements.
- Its easier to do this on a regular game by getting lots of other items but not the Water Orb.
- Do note that the boss here is not recruitable yet after battle since she is linked to another boss you are not aiming for..
- You have to do this if you're going for 0% Post Game as well

It is do-able with only reverse jump and wall kick to reach the boss area;
this is because you get improved jumping height from the water buoyancy.
You can only enter the boss room from the right though,
because trying to enter the boss room from the left is very difficult without the light orb and fire orb, which you don't have yet.


Took me sometime to stitch these screenshots together.

Its highly recommended you register the Natural Aquarium's Teleporter first,
as your only way out after defeating the boss is to backtrack out the way you came from.

The boss fight here is always the one with the highest lag in the game. Have fun.

==============================================================================

025) Take the upper path from earlier towards Icy Summit

026) You can do the Rita battle now since its along the way. I would teleport to Rabi-Ribi town and save game first, its better to be careful.

============================================================================

After beating Rita, you're free to continue into Icy Summit area, there are 2 entrances.

Register the Icy Summit Teleporter, battle the doppleganger of Rita, then battle Nixie.

Defeating Nixie gets you
*In some cases, you might not even meet the mysterious Rita clone as a boss battle in Icy Summit, not sure what triggers this, but generally, this does not have a major or game-breaking effect on your game.

Side chapter occurs when you have 6 people in town (if you followed exactly, you now have 7).
You should have the option for Rita vs Saya.
This gets you an acheivement.

You can also get another Rita-related acheivement, see section on Side Chapter encounters.

027) After the Side Chapter, try to look for the nearest teleporter, and warp to Rabi-Ribi town if you are not already there.
028) From Rabi-Ribi town, go right, your target is the Rabi-Ribi Ravine area, keep exploring higher and higher, and you should be able to find and battle Chocolate.
029) Find the nearest teleporter and warp to Starting Forest.

Go back to your early game route where you went non-linear.
============================================================================
Keep exploring, eventually the route is mostly linear and Erina + Ribbon strongly refuses to enter a certain area. Backtrack out of the place and you encounter............Cocoa boss battle.

Defeating Cocoa gets you============================================================================

Checklist so far:
- Never collected any items, except for the Cake + Donut that Rumi gives you.
- Never entered Miriam's shop in Rabi-Ribi town and never talk to her.
- Went boss hunting all the way without talking to Rumi.
- Already have 9 Town Recruits.

030) Your final sequence-breaking for the main game is to search for the 10th Town Recruit.
Go back to Rabi-Ribi Town, avoid talking to Rumi.
Walk around and you should get a trigger indication to search for Rainbow Crystal in Spectral Cavern. If it isn't that obvious, you are going to look for Ashuri.
Buy Cocoa bombs from Cocoa too, it will be very useful soon.

031) From Rabi-Ribi Town, teleport to Volcanic Cavern.
The path in Spectral Cavern is very linear, you will meet the boss battle almost immediately.

Rainbow Crystal Boss Fight FUN FACT:
- its actually a group of 7 mini-bosses.
- for each crystal you destroy, the remaining survivors will regain a bit of health.
- the crystals are always out of reach? SPAM REVERSE WALL JUMP and shoot Ribbon's Charged Attack at them, especially when they are together, its a very fun boss fight.
- Cocoa Bombs are really great here, it may insta-kill this boss, but game bug might also happen.

032) For beating Rainbow Crystal boss, backtracking gets youGetting 10 town recruits and never talking to Rumi for the entire trip since you went around recruiting gets you an acheivement.

================================
Backtrack to Volcanic Cavern Teleporter and warp to Rabi-Ribi town.
Now you can immediately continue with the game's plot by talking to Rumi.
The Bunny Amulet she gives you does not change Item %, and its importance will be very soon.



Talk to Rumi about the teleportation for the first time, and accept.

Cutscene, then boss fight vs Illusion Alius I (Erina + Ribbon doppelganger)
Very nice battle soundtrack too.

You get sent back to town.

When you're ready, talk to Rumi about the teleportation for the 2nd time.

Cutscene, then:
- Midboss fight vs 2 otaku
- Boss fight vs Illusion Alius II (2 stages, first you fight Erina clone, then Ribbon clone

You get sent back to town again.

Talk to Rumi about teleportation for the 3rd time.

- You get to move around in the area a bit. See section on CreSpirit secret base.
- Midboss fight vs 2 otaku.
- Midboss fight vs 3 otaku.
- Endurance boss fight vs Noah

(She has no health bar, you have to deal damage and survive for a short time)
- Boss fight vs Illusion Alius III

When you feel you're up to task, talk to Rumi for the fourth time.
This is the final part of the main game for Rabi-Ribi,
and is a boss gauntlet like the Elite Four challenge in Pokemon games.

- Return to the very first area of the game
- Boss fight vs Miru.

- Boss fight vs Noah.
- Boss fight vs Cyber Elf Noah (I've played Megaman Zero games and that's how it looks to me)
- Boss fight vs ??? (I think this form is what Noah wanted to be, or once was...not sure)

There is a big difference between a normal game and a 0% item game for Miru's boss fight.
You can damage Miru by one item in your inventory; the bunny amulet.

Cocoa bombs too, if you went and bought more.

Take not that you cannot spam the effects of the bunny amulet, it has recharge time.
Casual difficulty was recommended because bosses start out at very low levels with small increments for each subsequent encounter.
You meet Ribbon at Lvl 01, and if I remember correctly I met Miru with her being at Lvl 11.

Beating Miru, then Noah, then Cyber Elf Noah, then ???, ends the main game.

At this point, you get these 4 acheivements

============================================================================
Your town list at the beginning of Post-Game should look something like this

Most unrecruited bosses get harder after you complete Main Game.


By this theory then, after you have 10 people, and after the 3rd teleportation trip.
instead of going straight for the final battle vs Noah through the 4th teleportation trip,
you should go after the remaining people you have yet to recruit,

namely Cicini --> Syaro / Lilith / Seana,
and Aruraune / Keke Bunny.

See 0% Post Game section on recruiting these 6 people

With 0% and Bunny Amulet, you can immediately go for Aruraune and Keke Bunny.

Going for Cicini in the Main Game before beating Miru / Noah / ???, however,
will auto-nullify the Not Helping Ribbon's Friends acheivement if you don't have it yet;
so take note.

- 16 people (for those who already have the Not Helping Ribbon's Friends acheivement)
- 12 people (for those who don't have the Not Helping Ribbon's Friends acheivement)

If you've followed 0% Items Main Game section so far; then for Post Game we're left with:

--Missing 9 people from town checklist--
Starting Forest --> Aruraune / Keke Bunny
Cicini -> Syaro + Lilith + Seana
Miriam -> Rumi -> Irisu

You can find these 9 people in any order,
the listing in the 0% Post Game section doesn't really matter, but:

- Cicini battle must be done before you can go after Syaro / Lilith / Seana.
(EDIT: If you've followed the 0% Main Game section exactly, and the spring outside Cicini's room doesn't appear, try to look for Cicini again after Chapter 7 (Systemic Core - Red Area.)

- Irisu in most cases is usually the last person in the game you send to Rabi-Ribi Town.

For Post Game, if you see Cocoa in the Rabi-Ribi shop, feel free to buy consumable items to help your journey; (like Cocoa bomb and the desserts) but avoid buying other items. Time limit before Miriam's return to the shop is after you beat Rumi in Forgotten Cave II, so its best you stock up before then. The buffs sold by the people who you sent to town may be useful as well. Halo Buffs in Post Game have been said by the devs to be restricted to only Lv 1.

In Post Game, there is an increasing importance on Reverse Wall Jump + Wall Kick mobility, and the Bunny Amulet usage is used more frequently, mostly to avoid spikes. The devs also try to troll you into frustration by nullifying your 0% run in late areas of the game; you will understand this soon.


You can access the higher area of Spectral Forest (towards Aruraune + Keke Bunny) by another way, go back to the Piko Hammer area.

Be careful and avoid touching the Piko Hamer.
===========================================================================

The path from here onwards is extremely tricky because it it pure darkness without the Light Orb.
- You have to move slowly. (to avoid walking into enemies and spikes)
- You have to rely on sound to know if Ribbon's attack is hitting an enemy.
- There is one area in the darkness that Ribbon's attack can break a path, its very easy to find.

Do remember about the other spike area near a spring, once you see spikes in the darkness,
just use Bunny Amulet to immediately pass through and continue to Aruraune.

Getting to Aruraune may require a few attempts, but is not as hard as finding another person.
https://youtu.be/SlQdxZl8Jlo

By usual standards, you only need 22 / 24 people in Town to be able to reach Irisu at library.
Therefore it is highly recommended you skip Keke Bunny due to the Plurkwood difficulty on 0%.
If you still want to attempt it however, or if the game demands it, then read on.

If not, after getting Cicini / Syaro / Lilith / Seana / Aruraune,
you should go for Miriam / Rumi / Irisu track.

After getting Aruraune, backtrack towards the fork, use Bunny Amulet to pass through spikes, and go higher.

I have stitched together some screeenshots without the darkness for your convenience.

https://youtu.be/Qj-uGITdzDM
============================================================================

One thing to note; Keke Bunny is the hardest person in the whole game to recruit while on 0%.
You can explore the whole area with Reverse Wall Jump + Wall Kick, however,
- most of the enemies will be hazardous to your HP, so you should kill most, if not everything.
- there are 3 meatbone dogs you must not kill; they are important for progress.
============================================================================

============================================================================

============================================================================
- after you beat Keke Bunny, you cannot go back to the receptionist lady because she will force an item on you. And you cannot backtrack from Keke Bunny's battle arena because the platform is too high and spikes are in the way.

This means you have to go through the entire area for a 2nd time.
- on your 2nd time exploration, break through here for exit.
- leave Plurkwood and head back out towards Piko Hammer area.
- refer to the screenshot without darkness on avoiding the spikes


Keke Bunny is recruited when you talk to her in Rabi-Ribi Town.

============================================================================

Just teleport to Spectral Cavern, you don't need Rabi Slippers to trigger the quest, just time your jump direction over the spring right outside her room, and you can then battle / recruit Cicini.
If the spring isn't there, you probably haven't triggered Cocoa's scene yet.


When Cicini teleports you to Golden Riverbank and tells you to go to her lab through the lower route; unfortunately you cannot, the path is blocked a route which is only breakable by an item.

There is a shortcut you can find through a slight detour for the 0% path. See image beside.
===========================================================================
The 0% Items path for Exotic Laboratory.
===========================================================================

Once you reach the computer for the first time, Cicini will teleport you back to Rabi-Ribi town.
Try walking around Cicini or towards other save spots, (I tried by teleporting back to Exo Lab and going to the save spot at the bottom-right most of the map), and the quest to find Syaro should trigger. If it doesn't, try looking for other town members first.

When Cicini asks you to find Syaro, this is the breakable path towards Syaro you should take note of.

After beating Syaro, you have to backtrack out of the place by the way you came.
===========================================================================

See section on non-linear Lilith on how to get to her without items.
Teleport to Floating Graveyard, and continue onwards towards Sky Island Town.
Since you now have Ribbon's friends after meeting Cicini, you can continue with Lilith's 2nd battle in the air. (Ironically Erina flies using the hammer animation, even though she doesn't have it.)

See section on No Water Orb option.
Seana's recruitment only occurs after you battle her for the 2nd time in the west side of Rabi-Ribi Town.

The quest trigger for this should occur after recruiting 6 different characters;

• Cicini and Syaro (computer duo),
  
• Chocolate and Vanilla (Cat twins),
  
• Nixie and Nieve (Ice twins).

It may take some time.

Teleport to Volcanic Caverns, go towards Hall of Memories.
Use the teleporter, go to Rabi-Ribi Town and save, then come back here, avoid the Carrot Shooter and continue to meet Miriam.

If you can afford Miru's 25 000 en package of 11 buffs, you should get it, if you cannot afford it, go for the the individual buffs you can afford at the moment.
Or grind until you have 25k, anything goes.

On 0% items Post Game, Miriam's boss battle becomes hilarious since half her moves from summoning items is gone. You get an acheivement when she can't do anything for 10 times.

https://youtu.be/aOmrSe9mMJo
This leaves her offensive ability to summoning most of the previous bosses to do damage to you, which does include Miru. Good luck and have fun.
After beating Miriam, backtrack out.
I had to redo the entire Miriam battle because I walked into it on my way out..

============================================================================

Teleport to Starting Forest, head towards Forgotten Cave II boss rush area.
Have fun and good luck again, you'll need it.
The worst part of 0% Post Game in this area is the inconvenient location of the Bunny Amulet badge.



At the teleporter, do the usual, save at Rabi-Ribi Town, visit Miru and / or other people for useful buffs, get the consumables you need and come back. This should be the last time you are able to buy items from Cocoa in the shop before Miriam returns, so plan accordingly.

Rumi on Casual difficulty, 0% gets quite easy in the early parts.
Instant Death debuff is applied to most of her health bars, meaning Ribbon's default attack can massively deplete her HP really quick. You still have to avoid the aerial battles with Rumi in the air though...(this attempt would be easier if you've been practicing for Rumi's Dodge Master acheivement).
Instant Death debuff does not apply to Rumi's last health bar, the one without star symbols.
You have to survive her attacks and defeat her.
============================================================================

This is the path you're looking for while on 0% Items Post Game. A spring will appear that will let you enter the Red Area. The 0% item scriteria is strictly enforced for progress, it will never appear if not 0% items.
============================================================================

The Red Area this time has some differences, mainly:
- a lot of springs, almost everywhere
- a lot of paths that Ribbon need to break for progress

There's too many of these for a complete picture list; just assume if you cannot Reverse Wall Jump + Wall Kick, then use Ribbon to shoot everywhere and you should find something.

Sample picture

Most lasers can be avoided by:
- alternate paths by Ribbon
- standing in the gaps between lasers
- quickly breaking a wall or floor that hides you from getting hit by a laser
- excellent timing of jumping over a laser
- bunny amulet invincibility (though I would prioritize using this on the harder spike areas)
============================================================================
And once again at the end of a Post-Game area, the 0% exit is inconveniently placed near an item...
============================================================================

Teleport to Floating Graveyard, head to Library.
Strictly on 0%, a spring will appear that lets you enter the library.
============================================================================
I sure hope you do at least have some spare consumable items left in your inventory, because you will need it for Irisu..its also helpful if you've tried to practice Dodge Master for Irisu before this.

Beat Irisu and you win the game 0%.

Congratulations.

When you recruit 6 people to Rabi-Ribi town,
you get the option to teleport through the Stele for a third time.
==================================================================

The first thing you see should be a Crespirit billboard banner on the roof of a building in the background. This is the only other time in the game apart from the startup screen where you see this logo, so TAKE NOTE.
==================================================================

Proceed and you will see the game's self-reference.
==================================================================
Proceed and you will see an ice-cream shop.
The entrance to the secret base isn't exactly secret, most people tend to miss it because they just quickly walk past it. You should be able to get an "Enter" indicator at the right spot.
==================================================================

You need a Carrot bomb to continue through CreSpirit Secret Base, so this place is unaccessible on a 0% Items run.
All the NPCs here do not move, however they deal contact damage.
Take them out one by one for some interesting text.
==================================================================
One of the NPCs verifies the wall jump + wall kick technique;
in the speedrun mode almost all the Crespirit NPCs have different text compared to story mode.

You get an acheivement after visiting this place.

After beating Kotri at Floating Graveyard,
you can continue to Lilith's area in Sky Island Town.
but sadly you do not have enough jumping height to reach her boss fight place.
============================================================================
The solution feels like a joke.

With this you are able to meet / battle Lilith with default jump and reverse wall jump + wall kick.
You get an acheivement for this style of meeting Lilith if you haven't recruited anybody to town.
============================================================================

• Beat Ribbon boss at Spectral Cavern and/or Cocoa boss at Starting Forest.
  
• Beat Ashuri at Rabi-Ribi Beach. (not recruited)
  
• Beat Kotri with green powers at Rabi-Ribi Park (not recruited).
  
• Avoid Vanilla battle by walking along the roof. (not recruited)
  
• Beat Kotri with blue powers at Floating Graveyard. (not recruited)
  
• Proceed to Sky Island Town and meet Lilith.

You cannot get Lilith as the 1st Town Recruit, because you need Ribbon's friends from Spectral Cavern for the 2nd Lilith battle in the air.

https://youtu.be/DfjM5Cv0wwQ

Side chapter will always trigger when you have 6 people in town.
It will be Rita versus 3 of the people you have recruited.

With lots of non-linearity, and trying to reach as many teleporters without recruiting people,
I have done a few attempts to figure out the deciding factor.

• Rita -> Saya -> Pandora -> Cocoa -> Nieve + Nixie
  
• Rita -> Saya -> Pandora -> Kotri -> Cocoa -> Chocolate
  
• Rita -> Saya -> Pandora -> Chocolate -> Vanilla -> Cicini

The 3 orders above consistently got me the 2nd / 4th / 5th people as Side Chapter enemies

• Ashuri -> Cicini -> Cocoa -> Lilith -> Saya -> Chocolate

It got me Ashuri / Lilith / Saya as Side Chapter enemies.

From the 4 different sequences as above, it seems that the side chapter bosses are not randomized with who you currently have, but the 3 people Rita battles should usually be:
*If Rita is within the first 5, the order skips her since she appears by default in Side Chapter.

Senpai Noticed acheivement should therefore trigger if Saya is within the 1/4/5 order,
with some minor adjustments to account for if you get Rita within the first 5 people.
https://www.youtube.com/watch?v=sWvx7ixqe54

Do this when you have control of Rita; before the three enemies hit you.

For controller users, default keyboard "C" refers to the Piko Hammer / melee button.

It will look like Rita is spinning the fan in her hands really fast, and the acheivement triggers.

I've asked the devs about the time limit criteria, but they're not going to give it away easily...
What they can confirm though seems to be that different difficulties has scaled best par time.

I did casual speedrun and it seems the boss encounters scale in levels faster the more items I collect, compared to 0% item run. So only grab what you think is necessary.

The following is only one of several possible ways to do a speedrun;
it is not a must that you follow this exactly for best results,
you are free to experiment with your own styles for better results.

These two items are useful. Get them..

01) In Starting Forest, head towards Cocoa. Grab the hammer along the way, beat Cocoa and grab the carrot bomb.

02) Follow Cocoa into Spectral Cavern, meet and defeat Ribbon and she joins you.
Extra: Improve damage by getting the Poison Badge early.


03) Move as fast as you can towards Rabi-Ribi town.
Yes, you have to battle Ashuri at Rabi-Ribi Beach.
It is Ribbon's best offensive weapon for combos overall.
In Rabi-Ribi Ravine head straight for the next exit without delay.

10 minute limit to town is very manageable on Casual speedrun,
I'm not sure about the higher difficulties since you will spend more time on the boss battles.

Go into the shop & talk to Miriam, The item she forces on you is useful for speedy movement..

04) The extra 33% height jump is useful.
Steam user has found a faster way to skip the UPRPRC hideout.
https://www.youtube.com/watch?v=iI_1A1c-wGk

Low item % is helped (but not a must) if you look for items that boost Ribbon's offensive power.
=============================================================


Another player has useful tips.


05) Quite useful if you did 0% item run first as practice for speedrun attempts,
since by now you should be familiar with what to do and where to go.

Order shuffle:
Because you can go for items, go recruit Cocoa early from the Forgotten Cave since the Charge Ring for Ribbon is in that area.

Since you already have the Not Helping Ribbon's friends acheivement, you can go for Cicini & make use of the 2 times she teleports you. (to the East exit of Rabi Ribi Town and to Golden Riverbank)

• Piko Hammer
  
• Cocoa at Starting Forest
  
• Carrot Bomb
  
• Ribbon at Spectral Cavern.
  
• Toxic Strike badge above Piko hammer location.
  
• Ashuri Round 1 at Rabi-Ribi Beach.
  
• Sunny Beam

• Kotri with green powers at Rabi-Ribi Park
  
• Rabi Slippers in UPRPRC hideout.
  
• Vanilla at Sky-High Bridge
  (Town Recruit No.1)
• Auto Earrings at Floating Graveyard
  
• Charge Ring in Starting Forest; Forgotten Cave
  
• Cocoa Round 2
  (Town Recruit No.2)
• Cicini at Spectral Cavern
  (Town Recruit No.3)
• Defeating Cicini teleports you to the east exit of Rabi-Ribi Town, so Chocolate is the nearest.
  
• Chocolate at Rabi Ribi Ravine
  (Town Recruit No.4)
• Pandora at Golden Pyramid
  (Town Recruit No.5)

• Talk to Rumi & defeat Illusion Alius I (Cicini teleports you to Golden Riverbank after this)
  
• Ashuri Round 2 at Golden RIverbank
  
• Plus Necklace at Evernight Peak
  
• Saya at Evernight Peak
  (Town Recruit No.6)
• Nieve at Aurora Palace
  
• Rita at Azure Snow Land
  (Town Recruit No.7)
• Nixie at Icy Summit
  (Town Recruit No.8 + No.9)

• Talk to Rumi twice & defeat Illusion Alius II & III (to upgrade the Bunny Amulet)
  
• Buy Cocoa bombs if necessary
  
• Rainbow Crystal bosses at Spectral Cavern
  (Town Recruit No.10)

• Talk to Rumi for the final trip

See the link below for
speedrun video by Youtube user Daimon Dante

People keep saying it'll take about 10-20 hours to clear main game + post game together.
That's because you are zig-zagging all around until you have the proper mobility skills.

An optimum run to massively shave down that time, is to remember what the movement skills are, corresponding to what items, and where to find them in convenient order.

This is a regular game that's not aiming for the speedrun and 0% acheivements.

First, lets take a look at the skills and items.
=======================================================================

In corresponding relationships, we have these:

1. Once you clear the Prologue, be in Rabi-Ribi Town & already have
   Carrot Bomb + Piko Hammer,
   go to Rabi-Ribi Park, then UPRPRC hideout to get
   Rabi slippers.
   
   
2. Go to Spectral Cavern when indicated and battle Cicini,
   preferably getting her within the first 2 town recruits.
   
   
3. For the 2nd town recruit, I'd go for Vanilla at Sky-High Bridge.
   Make sure to look for the teleporter in this area so you can come back easily later.
   The actual aim is the teleporter in Floating Graveyard, as its the closest location to Lilith's area with the air dash which you can't get yet.
   
   
4. With two recruits, You should now go talk to Rumi for the first trip.
   
   
5. After this, Cicini should talk to you about heading to Golden Riverbank, and taking the lower path towards the Exotic Lab. Along the way, grab the
   Bunny Whirl item.
   
   
6. Get the
   sliding skill
   in the Exotic lab.
   
   
7. WIth the sliding skill + carrot bomb you can now go for the
   air dash ability
   in Lilith's area.
   
   
8. Re-explore the area where you went non-linear to meet Ribbon first before Cocoa, & get the
   Wall Jump item
   by sliding and Reverse Wall Jump + Wall Kick in the Spectral Cave.
   
   
9. From the Spectral Cave, you can go towards the Volcanic Cavern, get
   the Fire Orb,
   and use the teleporter to warp out. Rainbow Crystal boss will never trigger in Spectral Cavern so long as you never battle Ashuri at Golden Riverbank.
   
   
10. Take the upper path at Golden Riverbank towards Ashuri, while going towards Saya at Evernight Peak, you can get the
    Hammer Roll
    along the way since you can now break the block with Bunny Whirl.
    
    
11. From Saya's place, head to Aurora Palace and get the
    Water Orb.
    
    
12. With 4 recruits, talk to Rumi for a 2nd time.
    
    
13. After the trip, Cicini should talk to you about going to the computer lab again.
    Head to the computer cyberspace and get the
    double jump slippers.
    
    
14. With double jump and carrot bomb, you can now get the
    Light Orb
    in the higher area of Starting Forest.
    
    
15. You should now have all the items that help with your movement, congratulations.

After max upgrading your movement skills and Speed Boost at Miriam's Item shop in Rabi-Ribi town, you should be able to go anywhere quickly and easily, and be able to collect items almost as soon as you find them with no problems.



Once you have all the mobility items and start Post-game,
I highly recommend you to explore all the maps,
and get all the Health, Mana, Regen, and Pack Up items before going for the Post-game bosses.
=======================================================================

It is worth your time as it will make your encounters with the Post-game bosses easier.
If you feel that finding all the items on your own is taking too long,
there are already some map guides to help you.
http://steamproxy.net/sharedfiles/filedetails/?id=619938406
http://steamproxy.net/sharedfiles/filedetails/?id=620705295
You can't get all the badges and other misc items before defeating all the Post Game bosses though.

Simple theory, but very hard to pull off.

• Get Rabi Slippers.
  From UPRPRC hideout
  
  
• Get Wall Jump item.
  You need slide ability + Wall Kick skill to get Wall Jump item in Spectral Cavern
  
  
• Get double jump ability.
  From Systemic Core
  
  
• Get Air Dash ability.
  carrot bomb + slide before you can get item at Sky Island Town
  
  
• Have Bunny Amulet.
  At least one teleportation trip through the Stele

Do this in Main Game, preferably before starting Post Game.*
In the Systemic Core blue area, the path towards the red area.
https://www.youtube.com/watch?v=KIM-wXAseew
Once you reach that platform, just enter the room and acheivement will trigger,
no need to jump into the tunnel.

Your reaction speed must be very fast.

*Since the usual quest trigger to enter this area is the whole objective of Chapter 7, theoretically,
all attempts to trigger this achievement should remain valid until just before Rumi's boss battle in Chapter 6.

So if you are already in Post Game and haven't met Rumi for her boss battle yet,
go get this achievement first.

After getting the achievement, if you jump into the tunnel and fully explore the Red Area,
your game will be slightly broken in the sense that you can't get 100% items anymore..

https://youtu.be/Cq2Y9SERpMk

I have played quite a lot of games, mostly 2d side-scrolling platformers, and my enjoyment of Rabi-Ribi got quite a huge boost in seeing some familiar aspects every now and then.

==This is purely speculative guesswork on the developer intentions. ==
- Picture comparisons will come.
- Might be getting its own guide if the section gets too huge.

==Obvious so far:==

Megaman X5

Fusion of several genre(s)
Super Metroid + Castlevania: Symphony of The Night (SOTN) = Metroidvania
SOTN + Bullet-hell = Touhouvania
Touhouvania + bunnygirl = Bunny Must Die game on Steam
Average Megaman boss rush = 8 bosses
Rabi-Ribi has a higher production quality than Bunny Must Die for sure, and also adds in anime style Visual Novel cutscenes, expands on the boss rush known to Megaman (consecutively more than a dozen fights) and awesome soundtrack. I think Touhouvania is a more relevant comparison though...Wonder if that will be on Steam someday.
https://youtu.be/tJs7cPV5yyM

Good Smile Company Nendoroid Series

This is the average expectation of what nendoroids still in the box looks like.
The orange sticker is usually associated with GSC.

https://en.wikipedia.org/wiki/Nendoroid

Is The Order A Rabbit (aka GochiUsa) anime / manga series


Color theme and clothing are very similar,
while some other details like personalities have been mismatched probably to avoid DMCA.

GochiUsa's Syaro is scared of bunnies and has issues with money.
GochiUsa's Cocoa is friendly to the point of sisterhood,

Rabi-Ribi's Irisu loves bunnies and is worried about being too friendly.
Rabi-Ribi's Cocoa has issues with money.

Nekopara Visual Novel

Very obvious. Both are catgirl sisters, both have similar names, Vanilla is seen as the more serious of the two, and even the boss battle theme is of a humorous soundtrack.


http://nekopara.wikia.com/wiki/Chocola
http://nekopara.wikia.com/wiki/Vanilla
Vol.0 and Vol.1 of Nekopara are on Steam, while Vol.2 will be released soon.

Mario video game series.

Megaman Zero series.

Noah's 2nd form is reminiscent of the Mother Elf from Megaman Zero 2,
while the boss fight on a platform is akin to that in Megaman Zero 4.
(Along with the cyberspace area)
https://youtu.be/zFo_DCdzcv8

Rabi-Ribi's Illusion Alius boss is inspired by the first Megaman ZX game (or Megaman Zero 3)

The concept of:
- the player character fighting an improved enemy doppelganger version of the player
- distortion in time and space in the background
- epic soundtrack
- the boss fight itself can get very chaotic
- boss explodes when defeated
is the main theme to the Omega boss in Megaman ZX.
https://www.youtube.com/watch?v=SzGsFPEtZeM

Nisekoi series by mangaka Naoshi Komi; specifically the character Chitoge.

Reason for speculation:
Both Chitoge & Cicini have long, blond hair, and have a similar distinctive ribbon.
Both apparently come from a rich family.
Both of them are also quite cheerful, and strong.

Rabi Ribi's Icy Summit area is probably inspired by indie game Dust: An Elysian Tail, which is also on Steam. In that game there is an area where you climb up a snowy mountain, accompanied by fitting music.
https://www.youtube.com/watch?v=DFQGewcjngo
https://youtu.be/B82Xmil5n8I

Rabi Ribi's Hall of Memories is a reference to the Chaotic Realm in Castlevania: Aria of Sorrow.
http://castlevania.wikia.com/wiki/Chaotic_Realm

Similarities: Both are near endgame areas, the paths are mostly linear, and is a jumble of most of the previous areas the player has progressed through in the respective games.

The concept name Hall of Memories itself could probably be referencing Kingdom Hearts: Chain of Memories.

Rabi Ribi's Forgotten Cave II (the boss rush area) is probably a reference to the Cavern of Remembrance in Kingdom Hearts II: Final Mix.
http://kingdomhearts.wikia.com/wiki/Cavern_of_Remembrance

Similarities: Both places are deeply situated in a certain area, eventually leading you to fight powerful data replicas of previous bosses.

Note the opposite meanings of the naming in Cavern of Remembrance, and Forgotten Cave.
In KH2: Final Mix, you can choose which boss replica to battle,
In Rabi-Ribi, you have to go through all of them in one attempt.

The following people have in some ways helped contibute some useful information for this guide,
so this is where due credits go. =D