Nice fic. I could imagine this fic like it was actually in the manga. I'm not sure anime because I've only read the manga and never have seen the anime.

ish .. alrite..demo.. who's sakai ?

This story has lots of promise. I like how you decided to explore the story behind Sana's birth mother. I think you rushed the story too much and didn't really give the characters much time to develop both for the readers and with each other. I would really encourage you to expand on what you've already written and resubmit the fic. You have the potential to make this even better.

I thought your story was pretty realistic, and I'm glad you posted it. Keiko deserves a story of her own.

note: you didn't say you were switching times before "Ah a new book by Kurata Misako is..."