Just made an account to post here because I love this manga sooo much!

I've read every chapter thats out and theres something I want to say about Kirisaki (aka senpai)

In chapter 9 it was already revealed who her crush is. It was written very subtly, but you can get it out from the conversation between Fuyuki and Kirisaki:

Fuyuki is thinking in her head 'come to think of it the person senpai likes is...' and after she asks ".......is that the reason why you left home"
Kirisaki then tells Fuyuki that the trigger was when the two got married and she didn't want to necessarily see them happy. with "the two" she means her mother and her mothers boyfriend. Then she tells she couldn't see him as a father and she didnt like that he treated her like a daughter.
And going back on the "is that the reason why you left home", Kirisaki says "I think it was good I left home. After all if you dont see each other anymore, you'll have less time to think, although it might be lonely at first"

So what I read from this is that she left home because her crush, her mothers boyfriend, became her stepdad. She didn't want to see him happy with her mother and she didn't want to be treated like a daughter by her crush. Sucks for Kirisaki, but I think its very mature and considerate to the two of them to leave home and let go of her crush.

Still Kirisaki says she can like both men and women and for now she doesn't want to date.

Unpopulair opinion, but I'm rooting for Eri and Fuyuki. I see Kirisaki as a great friend and emotional support for Fuyuki, but I dont see a romantic connection between them. Eri on the other hand is about 1 or 2 confrontations away from realizing that her feelings are more than "Fuyuki is my bestie and its normal that I smile the most with her, want her to notice me, want her to see me as number one". So I look forward to see how Kirisaki will push Eri's buttons while also protecting Fuyuki from Eri's obliviousness.