At the moment, this is a pretty basic plot idea. The girls all end up going to the same college by some miraculous plot device, and hijinks (or hikinks?) ensue. Comedy and sex are the goals.
As for interactions, I like to imagine Yomi and Tomo having a private BDSM relationship with Yomi as the top, as a counter to Tomo's loudmouth silliness in public. I also imagine Kagura getting presumptuous with Sakaki. Chiyo, if she gets played, will have to be aged up a bit for the game - I'd say she could be 16 where everyone else is 19-20 at this point.
Koyomi "Yomi" Mizuhara (Karma)
Tomo Takino (Goalt)
Sakaki (Little Wolfie)
Ayumu "Osaka" Kasuga (ShadeofGray)
Potentially professors as well.
Ideas to give this game some grounding and direction are welcome!