Before starting, there's one thing you should know: there are more combination choices that will get you to the different endings than the listed below. But I've decided to put just an example of each one of the walkthroughs, as it's less confusing and they will give you the 100% of the game anyways.

Let's get to work!

Hikari Ending

Sorry, I’m just an empty carcass uncapable of noticing obvious things.
Well, I’m kinda sleepy.
Don’t worry, Hikari.
Go back to bed.
Leave
What about Hikari’s feelings?
Go back and study.
Resist your urges.
Tell Hikari you love her.
Ayame Ending

Sorry, I didn’t notice.
Yes, I’m ready.
Wow, you’re screwed.
Go back to bed.
Touch her.
You’re looking good today!
Enter Hikari’s room.
Try to approach her.
Resist your urges.
Don’t say nothing
Threesome ending

Sorry, I’m just an empty carcass uncapable of noticing obvious things.
Yes, I’m ready.
Don’t worry, Hikari.
Go back to bed.
Touch her.
What about Hikaris’ feelings?
Go back and study.
Resist your urges.
Go to Ayame’s room.
Tell her about Hikari.
Rape ending

8. Force her into having sex.