Something like the premise of Caste Heaven is the closest to what I'm looking for. Admittedly, it did give me the idea, though I can't say I enjoyed the aforementioned series much.

Basically, a student holds unquestioned, absolute power over their classmates. Bonus points if the power is abused and decided arbitrarily.

I don't mind bl/gl/whatever, but I'm definitely a little more tentative in reading those.

This is a stretch, but maybe Arisa. One of the students is 'king' (they don't know who) and this person grants requests that the other students send in on their cellphones. As I recall, the fulfilled requests start out innocent but get darker, and the king also has the power to declare people outcasts and then everyone else in the class turns against them.