This guide is the second in a series, intended to help you clear all five of Ikki’s endings and all of his CGs. First off will be some general gameplay advice, then some tips on dealing with Ikki if you’re struggling but don’t want to use a full walkthrough. After that is a step-by-step guide to Ikki’s good end, followed by instructions on how to get his four other endings. I hope you find this helpful, and do comment if you have anything to add!

Other Guides:
Shin
Toma
Ukyo

• I don’t think the options you choose before the route split matter terribly, but I’ll update this if I find out otherwise.
  
• It can often take a little while for your parameters to update after making a choice, so if you’re not sure you’ve picked correctly, it’s best to save before a choice and check what’s changed once you hit the next split or scene.
  
• Unlike some other visual novels, it’s entirely possible for your Affection and Trust to go down. This means you’ll sometimes be picking “safe” options which won’t appear to raise your parameters; this is because other options will wind up lowering them instead.
  
• Suspicion can also go up or down, and you’ll need to try keep it low for the Good End. To get the Bad End, raise suspicion while wearing Affection and Trust down. (Note that acting strangely around any character, not just your love interest, can raise Suspicion.) I’m not sure if there’s a hard and fast rule about Normal Ends yet, though, so just stick to consulting their sections.
  
• When reading the walkthrough, do note that not all endings require the same amount of choices. In particular, the full path to the Good End tends to have additional content.

• Ikki seems to like conversation options where you use his name, particularly in the first two weeks. For the rest of the route, though, there are one or two situations where it might be better to say something else instead.
  
• Boundaries are important to Ikki and he doesn’t want to pressure you, so don’t be afraid to tell him if he’s too close or otherwise being uncomfortable. Politely, of course.
  
• Be somewhat formal in dealing with him, particularly in the first week or two. Again, though, that doesn’t mean you should be difficult or rude.
  
• Questions you answer on the first day don’t matter up until you get Ikki’s call. If you’d like to skip the Orion babble, choose “Bag” when searching your room.
  
• Most choices in the first week or so, particularly the first few days, affect Suspicion rather than Affection or Trust. This includes the work scene on 02/08, which seems irrelevant but will make your Suspicion skyrocket if you mess up.
  
• Don’t be too coupley with Ikki on 20/08, or you’ll risk running headlong into Bad End 2.

This walkthrough involves choosing basically every "correct" answer, so you can modify it accordingly for subsequent runs. Bad Ends 2 and 3 come directly off the Good route, while you'll have to start new runs for the other two.

[01/08] Where would you like to go?
[01/08] Yes, I’ll go
[01/08] I would break up with him for sure
[01/08] You should’ve ignored those other girls
[01/08] You’re a little too close
[01/08] I’m okay
[01/08] Could you walk me to work tomorrow?
[01/08] Any option
[02/08] I’m sorry, I’ll get ready quickly
[02/08] Yes, please
[02/08] Good morning, Ikki
[02/08] Any option
[02/08] I’m sorry, I’ll try to hurry
[02/08] The customer is the enemy!
[02/08] Welcome back, Master
[02/08] I understand, Masters
[02/08] 2 coffees and 1 tea
[02/08] Um… I can stand by myself
[02/08] See you tomorrow, Ikki
[02/08] Actually, I’m not feeling well…
[03/08] I think we crossed the railroad
[03/08] Yes, sir
[03/08] No, it’s okay
[03/08] Ikki…
[03/08] Ikki…?
[04/08] Got it, I’ll stay away from him
[04/08] I do want him to stop
[04/08] It’s okay, don’t worry about me
[05/08] …It’s still a secret
[05/08] Let’s chase him
[05/08] Any option
[06/08] Oh, right, I did forget. What a surprise…
[06/08] What a surprise…!
[06/08] It’s okay, don’t worry about it
[06/08] What rumors have you heard?
[07/08] Are you ready for the 19th?
[07/08] Do I know them?
[08/08] Any option
[08/08] A month left for what?
[08/08] Okay, I’ll wait
[08/08] I’d be okay holding hands…
[08/08] Can I ask about Mine?
[08/08] Do you dislike me, too…?
[08/08] I wouldn’t confess
[09/08] Please stop!
[09/08] I’d definitely like to go
[09/08] (Choose all the options in any order you’d like)
[09/08] Any option
[09/08] Any option
[09/08] I, um…
[09/08] Maybe he feels lonely living alone
[10/08] Good for you
[10/08] I’m sorry…
[10/08] Um, you’re a little close…
[10/08] …The fireworks are pretty.
[10/08] Any option
[11/08] I’m going out with Ikki…
[11/08] What do you know?
[11/08] He told me to watch out for resentful people
[11/08] A Passionate Affair
[11/08] No, I wouldn’t dislike it…
[11/08] Yes, I’m free
[11/08] I think I’m okay for now
[12/08] How many people were going on the trip?
[12/08] …I can’t say more than I said before
[13/08] .........
[13/08] Orion, where are you…?
[13/08] Who is that man…?
[14/08] He’s my brother!
[14/08] Thank you, Ikki. That’d be nice…
[14/08] Do you like me, Ikki?
[14/08] Well… okay, then
[15/08] I think he’s liked me from the start
[16/08] I’ll do my best!
[16/08] Don’t worry, I’m plenty prepared
[16/08] …Okay, just wait a little while…!
[16/08] Um, I’m changed and in bed now
[17/08] Is there something wrong?
[17/08] Should I go over there…?
[17/08] …What happened?
[17/08] Do you feel better with me around?
[19/08] I’ll watch a little more
[19/08] I’ll pass
[19/08] You can stay
[19/08] Are you sad you can’t participate?
[20/08] …They only worked at first
[20/08] Not right now
[20/08] This voice…
[20/08] I don’t believe it anymore
[20/08] …
[21/08] Any option
[21/08] Please tell me your reasons
[22/08] Yeah…
[23/08] I won’t know if you don’t explain it
[23/08] …Why are you so mad?
[24/08] Ikki will be late
[24/08] What should I do?
[25/08] I’m sorry, but I’m working now…
[25/08] I think I’m in love with Ikki
[26/08] …
[26/08] And if your eyes worked on me…?
[26/08] …You’re special to me, too
[27/08] I don’t want to go…
[28/08] …Could you give me a hug?
[29/08] I was interested in their club activities…?
[29/08] How long have you known Rika?
[29/08] …Rika threatened me

I won’t lie, getting the Normal End took me literally hours of trial and error. I kept hitting one Bad End or another, and I was afraid if I gained too much Affection and Trust I’d wind up with the Good End again. It's a little more complicated than I first thought, but still pretty manageable: you'll need to keep Suspicion down to avoid Bad End 1, and Affection/Trust a fair bit above medium to avoid hitting Bad End 3. You'll also still need to choose "I think I'm in love with Ikki" on 25/08 to do the same. To cement it, give Ikki a different answer when speaking to him on 26/08, and do the same for Toma the next day. (Thanks to AlexHusky and TsundereHime for setting me straight.) You’ll know you’ve gotten there when you receive a call on 28/08 from an unknown number, and you’ll get a different CG and epilogue. At least it’s a really good one.

[25/08] I think I’m in love with Ikki
[26/08] Any option
[26/08] ...You're special to me too
[27/08] …I haven’t decided yet

Raise your Suspicion whenever possible by screwing up at work and acting strangely around Ikki, Sawa and Toma. You should try not to gain much Affection or Trust, but it’s best if you actively manage to lose some. You’ll know you’ve gotten it when, on 16/08, Ikki drags you back to his house and confronts you.

[16/08] …I don’t remember.
[16/08] No, please, stop!!

A straightforward wrong-options ending, which requires making a couple of poor decisions. You should be able to get this as part of the Good route.

(Want to go over to him?)
[20/08] Yes
[20/08] …Yes, I’ll try
[20/08] Any option

Another ending which you can get in the Good route, so play normally and save before the choice. It’s also the ending you get if you don’t have high enough parameters for Good, but this way is easier: just say you don’t return Ikki’s feelings when prompted.

[25/08] …I don’t dislike him, but…