Toge Inumaki is important too. His special cursed speech ability makes him stand out. Also, the principal of the school, Masamichi Yaga, is likely to be important as he is in a position of authority and has an influence on Gojo and the other students. There could be other characters like the members of different clans that also play roles in the complex web of the story.
Cursed fanfiction is a type of fan - created writing that often contains very strange, disturbing, or unconventional elements. It might involve combining characters from different universes in really odd ways, or putting them in situations that are completely against their normal character traits. For example, making a cute and friendly cartoon character into a villain in a very dark and twisted story.