Dream game? (Oh dear God, here I go with this idea)
Well, I would say something like a Touhou version of Space Channel 5 where Iku/Patchy (Cookie for the people who understand why Patchy) is the main character. The story line would be allong the following of a dance competition in Touhou and the winner will get one wish(corny, yeah, I know :fail:). A stage would go like in Space Channel 5 where you just try to clear the stage's rules. At the boss battle, you end up in a danmaku dance battle where you follow the pattern to dodge/graze your opponent's danmaku, while firing off your own. The game would inclued all of the girls, and you can take a certain people with you to a dance off against each stage, which would allow you to use their spell cards to help you out. Multiplayer would be one-on-one where in a set period, a player would make a rountine, where the other would copy and make one of their own. After each stage, players earn points for Rinnosuke's shop where they could spend their points on stuff like alternate costumes/special features.