At some point, several hours in, the game will change all of its currently available sidequests. Any sidequests you have ongoing but haven't completed, will be removed from your quest list and unable to be restarted. The repeat playthroughs required for the other Endings will all start you off after this change, making one achievement (The Sheep Whisperer) unattainable on that save if you don't do it early. (Though Ending E does require a completely fresh save file, where you could still get it)

There is no warning as to when the transition is coming. But, if you want a general hint:
When you recieve a letter from the Mansion, you are getting relatively close. Now's a good time to start finishing up any early side content you want done. You still have room to progress the main story a bit though.
If you want the exact point the shift happens: It is after you pick up the Vapor Moss by the waterwheel. After you complete that action, you will be unable to do anything other than the main story for a period, and the sidequests will change.

The Fisherman's Gambit sidequest is the only exemption to this, that will stick around.

You will unlock 14 achievements just by following along with the story and completing all endings. These are not listed here, for obvious reasons.




Man of Means
Hold 1,000,000 Gold.

Yup, that's exactly as grindy as it sounds. It's in your best interest to avoid buying anything at all during your playthrough (outside of Weapons and upgrades of course). You will get more health items than you'll ever need from world drops alone.
Past that, the best options for grinding money are to repeatedly run the third door in the World of the Recycled Vessel (See Dear Diary Achievement), or just gain currency passively as you farm for weapon materials for the All Upgrades achievement. You can save your game, sell absolutely everything you hold, and quit without saving after the achievement unlocks.


Wordsmith
Collect 50% of all Words.

Enemies will naturally drop these as you go. You'll collect a large amount of them just from your first playthrough. If you go for all endings, you should get this achievement in Route C at the latest. If you somehow still don't have enough, you can gain unlimited access to a fight arena by completing the The Magical Stone quest. A few runs through there should eventually tip you over 50%.


Weapons Collector
Collect all Weapons.

You already need to do this to see Ending C. Check the Weapons section further down for the location of each weapon. This does not include the weapons in the 4 Yorha DLC.

Upgrade Apprentice
Upgrade 5 weapons to Level 4
Reform Specialist
Upgrade 15 weapons to Level 4
Forging Master
Upgrade 33 weapons to Level 4

I hope you enjoy grinding! This is a long and arduous one, but there is one small shortcut you can take advantage of at least. The achievement is based on a fixed amount of 33 weapons, the amount the game usually has. But if you download the free 4 Yorha DLC on the store page, four new weapons will be added to your character with significantly easier upgrade requirements. That will at least let you skip four of the grindiest weapons. (Most people seem to recommend skipping Axe of Beheading, Spear of the Usurper, The Devil Queen and Sunrise)
Past that, unfortunately it's just a matter of grinding. There is this extremely useful site[videochums.com] to help though. Enter the current level of the weapons you have, and it'll give you a complete list of all materials you'll need to find to fully upgrade them. I'm afraid it doesn't have the requirements for the 4 Yorha DLC weapons though. For those, you need:

4 Rusted Clump
4 Goat Hide
8 Crystal
9 Dented Metal Board
5 Titanium Alloy
8 Amber
6 Memory Alloy
7 Severed Cable
4 Moldavite
4 Iron Ore
3 Silver Ore
3 Gold Ore
1 Large Gear

Once you know everything you need, it's then just a matter of collecting it all. This guide should be useful in finding the location of each material:
https://steamproxy.net/sharedfiles/filedetails/?id=2470017058

These are the main cause of the spoilers in the achievement section. Kill each of the game's bosses in a certain time frame. A few are very heavy spoilers, and they're not hidden whilst other achievements are. It is mostly safe to look at these after you finish Ending A, but be aware there is one minor spoiler to a boss in Route C.

Anyways, the way to get this should be obvious enough. By the time you're on your Route C playthrough, you should be dealing significantly more damage to each boss than you were originally meant to. It should be no challenge to shred through their health and leave plenty of time remaining for the achievement. If you don't see the achievement, just reload your save.
Irritatingly, cutscenes and Character Novels are also counted as part of the boss's timer. Spam Start or Escape to skip them as soon as they appear (And choose "No" when it asks if you want to read a character novel again) until you're back to regular gameplay. The achievement should then trigger.

Route B adds extra dialogue to the boss fights, and you will miss it if you rush. Wait for Route C before attempting this achievement.
Route C will also add some extra cutscenes to the bosses that reside in the final area. So you'll have to wait until your Ending D run for those if you don't want to miss those.

Read after Ending A: The Mermaid boss also has a speedrun achievement, but is hidden while the others aren't for some reason. It can only reasonably be done in Route C, where the fight will have a slight change.

⠀⠀⠀⠀⠀⠀⠀ Village Handyman
Complete 10 Quests
Jack of All Trades
Complete 20 Quests
Go-To Guy
⠀⠀⠀⠀⠀⠀⠀ Complete 30 Quests

Thankfully, there is no "Complete all Sidequests" achievement, and there are many more Quests in the game than the 30 required for 100% achievements. Even after the Sidequest changes, there's still more than 30 available. So even if you rush the start of the game and don't do any side content, you'll still be able to get this achievement afterwards.
Check the Recommended Quests section further down to cut down on filler and save your resources: You need those for the weapons!

Combo Fanatic
Reach a 50 hit combo.
Combo Master
Reach a 100 hit combo.

Both of these can be acquired naturally through gameplay, but the second is significantly more difficult. There is an easier method: The Tale of the Study sidequest, given in the Mansion. This quest involves killing a single extremely high defense enemy that does not fight back. Equip a low damage weapon if you want to be certain not to kill it early, and go to town on it. You should reach the 100 hit combo with ease.


Dear Diary
Complete the World of the Recycled Vessel

Recycled Vessel was a DLC for the original game, now integrated into this remake. After completing Route A, an interact point will appear beside your bed in your house. Use it to enter the Recycled World, where you'll fight five waves of enemies in three separate sequences. Depending on how many side quests you did, you may be able to beat the first two doors right from the start. Abuse Executions as much as you can: Use magic that knocks down enemies, or the held Heavy attack of a two handed sword. Dark Gluttony is an amazing piece of Magic to use here, as enemies tend to fill the entire arena with projectiles.
It's recommended you don't attempt the third door until you are at least level 33 or so. The last two waves have multiple bosses that can instantly one-shot you if you aren't high enough level. Spam healing items, Equip your best Words, and keep your distance and use mostly Magic against the Boss enemies to avoid the risk.

Fish of Legend
Catch a Rhizodont

Brace yourself, this is a long one.
First, you need to finish all the Fisherman's Gambit quests to gain the max fishing level. Check the The Fisherman's Gambit section further down for advice on them.
Then, stock up on Sardines. You can fish for them if you really want, or just buy them from the bait store in Seafront. Fast travel to the Desert, and start fishing with your Sardines there. Wait for the lure to dip twice, then stop. If it goes under on the first or second dip, then just wait and let your bait get taken.
After the pause, the lure should suddenly go under and you're guaranteed to either have a Sandfish or Rhizodont tugging on the line. Reel it in, and watch the bar: If it's not moving extremely slowly, then you don't have the Rhizodont on the line. If it is the Rhizodont, focus and keep at it. It'll take around a minute of constant pulling to finally fish it out, but the game is pretty generous with the time before your line breaks, so don't stress too much.
The Rhizodont is pretty rare, so don't get disheartened if you go through a large amount of bait and don't see one. It took me around 30 Sardines before finally catching mine.


Material Hunter
Collect 50 Different Materials

Another achievement you really should get naturally over the course of the endings. This one is easy enough that you should get it during Route A. You really can't miss it unless you're deliberately not picking up materials or something. If you somehow are still missing this achievement, you'll get it while farming for the Forging Master achievement.

The Sheep Whisperer
Only available early game!
Kill 100 sheep

Sheep stop spawning after the sidequest shift, but thankfully this achievement is really fast to get, even on a fresh save file. Simply run out of the Village into the Northern Plains, and immediately after loading pause the game and choose Orders > Animals > Call. This will whistle and cause all animals in the area to move towards your position. Run into the main field and you should have a decent amount of sheep already gathered around, or stuck on the walls. Move behind them so they don't run too far away, and kill as many as you can. Don't worry about killing every sheep you see, it's not worth it. Once you've got all the sheep that are close, run back to the Village, and repeat. Five or six times should be enough to get this achievement.


Daredevil
Ending E Spoilers!

Peek under Kaine's skirt ten times. Move your camera as low as it'll go, and try to frame Kaine on the right side of the screen for the best angle, then leave your controller alone. You'll know you've got the angle if Kaine starts making direct eye-contact with you. After a few seconds she'll play an animation and knock your camera away again. Repeat 9 more times for the achievement.

Ya pervert.


Legendary Gardener
Cultivate a white Moonflower

Welcome to Nier: The celebrated Hack and Slash RPG/Flower Breeding Simulator!
Yes, you may have played the whole game without noticing it, but there's a whole flower crossbreeding system at play in your garden, and you need to put some time into it for this achievement. First, make sure you've unlocked your garden and all additional rows through the Shopping List and A Return to Shopping quests. If you're already on Part 2, you can can unlock it by buying a Cultivator's Handbook from the florist instead. Then stock up on Red, Gold and Blue Moonflower seeds from the Grocery store in Seafront.

Plants will grow 24 hours after being planted, and then wilt 48 hours after they sprout. Yes, that is in real time. You can change your system clock to speed things up if you don't want to wait. By planting flowers in a specific order, you can crossbreed them together. There's also an element of RNG, in which they'll just fail to crossbreed entirely. Fun.
Whenever you successfully crossbreed a flower, immediately plant its seeds and use some Bounty Fertiliser on it to increase your supplies and save yourself from having to repeat steps constantly. If the crossbreed fails, just try again.

Plant RED GOLD RED GOLD RED along a row to get Peach Moonflower seeds.
Plant GOLD BLUE GOLD BLUE GOLD along a row to get Indigo Moonflower seeds.
Plant RED INDIGO RED INDIGO RED along a row to get Pink Moonflower seeds.
Plant PEACH PINK PEACH PINK PEACH along a row to get a White Moonflower, and probably leave Nier questioning his life choices.


A Round by the Pond
Catch all Fish

As with the Rhizodont achievement, you'll want to have completed The Fisherman's Gambit quest in order to gain max fishing level before attempting this achievement. Ideally you'll catch a few of the fish you need in the process too. In order to get this achievement, you must fill all entries in the "Fishing Records" section of Grimoire Weiss's Notes page. This means all 15 fish need to be caught, not just purchased. After completing The Fisherman's Gambit, the "Fish of Legend" achievement and catching a Shaman Fish for the storyline, there should only be four more fish to catch:



All Aboared!
Ride a boar for Five minutes.

You don't need to control the boar, just sit on it. If you can't ride Boars yet, you need to complete the Boar Hunt! Quest.



Light Speed Fighter
Beat the game (Route A) in 15 hours.

Ending E doesn't count for this I'm afraid, no cheating! This is a straight run from the very beginning of the game to Ending A. Set the difficulty to easy, skip all cutscenes and just sprint directly to each story point. It's not hard to get, if a little boring.



The Final Verse
Earn all other achievements.

I hear there's a particular guide that can help with this one...

A note: Don't expect to have many of your questions answered by the main endings. Yoko Taro loves to spread his stories across types of media, and Nier is no different. This game focuses almost entirely on the adventure of the Main character and his companions, and very little is explained about the world or what brought it to this state. The rest of the story is written in books, audio CDs and stage plays (yes really).
See the Additional Materials section for ways to view this extra material, and gain some understanding as to what's actually going on.

Nothing complex to do here at all. Just play the game to the end, and enjoy the ride.
Once you finish the game, save over your file when prompted.

Select Continue on your file you saved over, the game will resume from an earlier point in the story.
Requirements are the same as Ending A, just play to the end again. There will be some text sequences, additional dialogue, and extra cutscenes now added throughout the game. With your higher level, you will cleave through the health of bosses. Take some time and just dodge around at the start of each one if you want to hear all the extra dialogue.
Once you finish, save over your file again.

Again, continue from the same save file. You can safely skip the cutscenes to save time at this point. Route C adds a few extra, but they're shown as dialogue boxes, so you can't accidentally skip them. There is an additional "Novel" sequence after one of the bosses in the final area. You can't skip it so don't worry about missing it. Though if you're going for the Speed kill achievement on the boss, it does still count on the timer, so start mashing!
Before you enter the final area, use the postbox beside the door to make an extra save in another slot! This will save you running through the entire game a fourth time for Ending D.

You need to collect every weapon in the game before entering the final area. Use the Weapons section further down to find the ones you're currently missing. After the final boss, the game will now continue.
You will be presented with a choice at the end. Choose the top option. Do not pick the bottom option first!

After ending C, load the save file you made before entering the final area, and read this spoiler:
This ending will delete your save file! You can backup your save in advance from the paths listed here.[www.pcgamingwiki.com]. I'd really recommend you finish Ending E before attempting to restore your old save though, it's not long.
Play to the end again, and choose the bottom option.

This ending was intended to be included in the original game, but cut due to budget constraints and was published as a short story instead. The remaster finally adds it to the game proper, and is considered the Canon ending of the game.
After completing Ending D, make an entirely new save file. Play through the game from the beginning again, and eventually the game will transition to Route E. You can use this playthrough to get any Part 1 achievements you missed if you want.
You can't miss the transition, once you complete Ending D the trigger is set and it's guaranteed to happen. If you want to know exactly when Ending E begins: It is after you kill the Lizard shade with Kaine, the second time you visit The Aerie.

After you complete Ending E, any other new save files you create will continue as normal again, without the transition into E. Though, if you watch Ending D again, it will set the trigger again too.

An unfortunate relic of its design, Nier Replicant has many quests that only serve as filler content. Speak to client, get a few lines of dialogue, a list of resources to deliver, then a reward. The vast majority of these quests have zero relation to the story, and some ask for annoying to collect or rare items. You need to save all the resources you can for the Weapon Upgrade achievement, it's really not worth doing any of these quests. Remember, you don't need to complete all Quests for 100% achievements, only 30 of them!

Below I've listed the quests in each Part that I do recommend doing. These are either easy to complete, have ties to the main story, or just provide some entertainment. I've also separately listed the quests that at least aren't resource-sinks, but you really won't be missing much if you skip them.
You can speak to Devola in your town's Tavern and she will give you a list and location of any sidequests you currently have available to pick up.

Remember that you will permanently lose any of these you haven't finished after the Sidequests change!

• Old-Fashioned Home Cooking: You need to kill 100 sheep for an achievement anyway, and this lady will continually buy any mutton you give her after finishing the quest. Might as well accept this quest for some extra gold as you complete the achievement.
  
• Shopping List: Unlocks the ability to plant flowers in your garden. Required for an achievement.
  
• A Return to Shopping: Increases the size of your garden.
  
• Boar Hunt!: Gives you an item that allows you to ride boars, significantly speeding up your travel through the Northern and Southern plains. Early game, the boar is a dangerous opponent, able to kill you in only one or two hits! Use Dark Lance to interupt its charges, and keep your distance.
  
• Yonah's Home Cooking: You can get Venison from the deer in the Southern Plains, and Wheat from the Grocery Store in your village.
  
• The Ballad of the Twins: The ingredients can be irritating, Mouse Tails can be found only at the Junk Heap entrance, and Lizard tails in the Eastern Road or around the Northern Plains. You need to pick up the animal, not attack it.
  
• A Dog Astray
  
• The Postman's Request
  
• The Lighthouse Lady's Wrath: Tied to above.
  
• Closure: Tied to above.
  
• Yonah's Gift: Melons can be bought from Seafront Grocery, Watermelon and Pumpkin from Facade's Grocery.
  
• Letter to a Lover: Unlocks a quest in Part 2.
  
• The Runaway Son
  
• The Missing Girl: Unlocks a quest in Part 2.

• The Gatekeeper's Errand
  
• Book Smarts
  
• Fragile Delivery: Fairly easy, just run to The Aerie and jump over enemies as much as you can. Watch out for the Bats in the cave at the entrance! There are other Fragile Delivery quests after this one, but they are more difficult. The only reward is Gold each time, so don't worry about missing these.
  
• The Tangled Message
  
• Apology from a Fool
  
• The Littlest Hero

None of these quests are missable. You can do as many as you want on each repeat playthrough.

• Thieves in Training
  
• The Strange fate of the Jewel: Relates to the Lighthouse Lady quest chain.
  
• The Damaged Map: Weapon Reward, Labyrinth's Shout. Required for Ending C/D. You may want to find a guide for this one.
  
• A Bridge in Peril: Weapon Reward, Labyrinth's Whisper. Required for Ending C/D.
  
• A Tale of the Study: Easy way to get the 100 hit combo achievement here. There is also a small extra line of dialogue if playing on Route B.
  
• Research Project: Immediately given after A Tale of the Study. Leave and re-enter, then speak to the quest giver again.
  
• The Promised Gift: Do this as soon as the Ferryman offers it. Additional content added in the Remaster disables this quest after a while.
  
• A Shade Entombed Required to unlock the next quest.
  
• Disturbing the Sleep of Kings: Weapon Reward, Labyrinth's Song. Required for Ending C/D. You need to go back to the original Boss room of the temple.
  
• Shadows of the Desert: Only available if you completed the The Missing Girlquest in Part 1.
  
• Search for the Shade
  
• Freesia: Only available if you completed the Letter to a Lover quest in Part 1.
  
• The Despicable Man

• The Scattered Cargo: Offers a discount in Seafront stores or a large amount of Gold. The gold is the better option, as you shouldn't be buying anything other than weapons from stores normally.
  
• Master of the Southern Plains
  
• A Child's Final Chance
  
• The Great Tree
  
• The Shade Army
  
• Nightmares and Dust: Search around the center area of the sandstorm.
  
• The Magical Stone: Weapon reward, but you'll also have this weapon added to your inventory on Route C anyway. This quest does have a slight link to the story, but it also requires you to climb all the way to the door to the final area and back to the quest giver again. If you do decide to do this quest, make sure you pick up the weapon from inside the building during the fortune telling sequence.

This is the only quest that will persist through the entire game.

This quest is required for the Legendary Fish achievement. And I'm afraid it's a long one. You will need to catch Nine different fish. The amount required starts high, but fortunately gets lower with each quest. I found the start was the most annoying part, but things get better as you go along.
The first 5 quests are available immediately in order, the last 4 will only be given after advancing the story far enough.

The first 8 weapons are available at all times. The rest are only available after story progress.

All weapons after this point are only available after Nier gains the ability to wield their classes.

So you finished the game, you saw an ending, but you're still left stumped as to what the hell is even going on. As I mentioned in the Endings section, the game has very little to offer in terms of answers to its overarching story. That is all stored in the additional content that was released alongside the game.
But of course, not everyone wants to spend hours reading just to begin to understand what they've gone through, so the sources below are arranged in order of how much "commitment" they require.

For most people, I'd recommend just watching Drakengard's Ending E, complete Ending B of the game, and then follow up with BrandoSP's Lore videos for the best experience.

The content linked in this section is safe to watch at any time
Drakengard is a Dynasty Warriors-esque hack and slash game for the PS2. Set in the dimension of Midgar, it tells the tale of a Soldier and a Dragon, brought together in a time of war. The story gets very dark and very strange, especially towards the game's final stages. Like Nier, it had multiple endings to achieve. The final one, Ending E, was originally designed entirely as a joke: But eventually was adapted into the story we have in Nier Replicant.

I'll be entirely blunt and say that Drakengard as a game is pretty terrible. Even disregarding its age, the game's combat is clunky and slow, the weapon unlocks are difficult to find and often have nonsensical requirements, and the entire thing becomes repetitive extremely after the first few levels. I would absolutely not recommend playing it yourself just to see the connection to Nier, which ultimately isn't all that detailed.
Instead, I'd highly recommend watching this Let's Play series by Rasen Bran. He frequently explains the game's deeper meanings and elements of its original Japanese release which were censored or not alluded to for... Obvious reasons.

To reiterate though, Only Ending E relates to Nier, and it was originally made as a joke. It's a single event that takes about 30 seconds to play out. If you don't want to watch an entire Let's Play, you can watch just the ending here: https://www.youtube.com/watch?v=6OPW-RdzStA

The "Investigation Report" and "Project Gestalt" chapters are safe to read after Ending B.
The short stories and other content should be left for after Ending E.
Grimoire Nier is a Japan exclusive companion book for the game. Containing several short stories, character profiles, concept art, and interviews with the developers. This is where the vast majority of Nier's story is finally explained. There are other elements in audio dramas, interviews and plays (Because Yoko Taro is a very strange man), but the most important parts are at least included in this book.
An English version was never released, but thankfully a fan translation is available.[docs.google.com] It's the work of multiple translators from across the internet, so the quality can vary in places, but it's all readable enough.
The short stories are hosted separately. You can find them all on the wiki.[nier.fandom.com]

The first two videos linked below are safe to view after Ending B.
Don't want to spend hours reading through multiple stories and vague in-universe reports? Still want to experience some level of storytelling rather than have all the answers thrown straight in your face? For that I can provide BrandoSP's Nier Lore series.
He takes the mess of events and details from all the material Yoko Taro has released, condenses them down to only what matters, then pieces them together into one easy to follow timeline of events. Plus it has a decent dose of humour to it. I'd honestly recommend all the Nier videos on his channel (After finishing both games, of course!) but for just the untold backstory of Replicant, you only need two:
Start with his timeline video, then watch the dedicated Project Gestalt video.
https://youtu.be/gaIlfMyXVNA
https://www.youtube.com/watch?v=O3oMH4dnGrc
There's also a third video about an Audio CD story that was never released outside of Japan. It's not required to understand the main story, but it does provide some great extra detail to two characters. Spoilerish Title Hidden

He also has a video on the near impenetrable background lore to Automata (Yes, somehow it's even worse than Replicant), but bear in mind that this video drops heavy spoilers for all of Replicant and Automata. Do not watch until you have fully beaten both games!

The Recommended Articles linked below are safe to view after Ending B
Finally, if you just want everything explained concisely, or there's still some aspects you don't understand, the Wiki has everything laid out clearly in individual articles.
Be aware that content related to Nier Automata is also hosted here. I don't recommend viewing any pages outside of the ones linked if you haven't played it yet. There are massive spoilers in many articles, and some in just the images.
Also, Fandom/Wikia is a terrible site! Don't scroll down too far past the bottom of the page or it'll start showing "Recommended Articles" which can of course, show more spoilers from their title and image.

I recommend starting with these articles:
Shadowlord[pastebin.com] (Cut from wiki page due to Automata spoilers)
The Giant[nier.fandom.com]
White Chlorination Syndrome[nier.fandom.com]
Red Eye[nier.fandom.com]
Replicants[nier.fandom.com]
Gestalts[nier.fandom.com] (The Project Gestalt article has major Automata Spoilers!)