You know, I think the reason games had unlockable costumes as bonus content was because it was something that was pretty quick and easy to add. (In some cases, those other costumes might have been made anyway for a beta version)

So, if you're gonna propose a game idea that won't be made anyway, why not let your imagination run wild?

When beating the game you can unlock 4 costumes you wear in her locker. The first costume is a regular outfit, second is a gym uniform, third is something cute and funny for a school play, and fourth is a red dress for a school dance.