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.
If you like League of Legends, I recommend you to read the novel "Mobile League of Legends: Exodus". The main character, Ji Luo, unlocked his hero and skin by spending money, obtained all his skills, and traveled through various worlds in the game. In addition, after he leveled up, he could also use the file fragments to synthesize a new skin to achieve the goal of upgrading his skin. If you're interested, you can go take a look.😋I hope you like my recommendation. Muah ~