So, I was thinking about this scenario:

There's a special "all-girls" school, in which the students are divided into three "castes", so to speak:

The Girls are top of the food chain. They're well-built, well-endowed, conventionally attractive, fit, etc. They enjoy a lot of privileges, the biggest one being their diapers. They all wear diapers, which give them the privilege of relieving themselves wherever they want, leaving it to someone from the lower castes to clean them up. Each Girl has also has her own, spacious bedroom.

The Dorks are girls who don't fall into the category of "conventionally attractive." They're short, flat-chested, usually have thick-rimmed glasses and/or braces. They're academically pretty gifted, and usually are into "loser" hobbies, like video games, comic books, scifi, fantasy, and so on. They wear pull-ups, which they can use for pee, but if they need to go "number two", they have to use one of the many adult-sized plastic potties that are standing all around campus, in plain view of everyone. But at least, they can order members of the lowest caste to change their wet pull-ups or wipe their bums after going potty. They also have to do the Girls' homework, and can even be made to take exams for them, and are punished for bad grades. Each Dork also has to share a room with a member of the lowest caste, and those rooms are smaller than the Girls' rooms.

The final, and lowest caste are the Sissies. They are "men" who are sent to this school because they are considered not masculine enough. Too weak, too submissive, not athletic enough, not masculine enough. They have to wear the same uniform as the Girls and Dorks - blouse and skirt - but instead of diapers or pull-ups, they wear panties, which means they have to use the public potties for everything, and are often mocked for not even being able to pee discretely.

I would play a Sissy, you would play the Dork who lives with me, and we both would play all the Girls and staff and faculty our characters interact with.