Possssible former dating shenanigans with Rei. She'll be 20-21ish, a molecular biology undergraduate, sheltered and reserved, but not nearly as much as her original. I could see them sharing a general requirement course and getting to know each other if Sasame took the initiative. It would probably be her first romantic relationship that wouldn't last the whole semester because, at least on her side, she'd put more attention into her work than him. And, on her end, it would end calmly and act as an eyeopener to that part of life to her.

lmk if you're interested! I haven't apped her yet so I don't want to get too detailed.