Hello!! Being canon-familiar with Mimi I think that's pretty correct and Rise's original personality would mesh well with Mimi as well so it would be some really fun CR!

I like the idea of them being related as cousins, but I would like to just cross-check with the other members of Rise's AU family! Hinata Aoi from Ensemble Stars (livens) is her younger brother and they have a cousin, Miyamura Izumi from Horimiya (akatatai) who's about the same age as Rise and Mimi, and Hinata's sixteen iirc as well. Let me confirm with those players really fast and see if it'll pan out but I'm sure it'll be fine <3