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.
Well, it could be about a BTS member accidentally running into a gymnast YN at a sports event. Maybe they get to know each other gradually and BTS is inspired by YN's dedication in gymnastics. It could also involve YN getting a chance to perform at one of BTS's concerts, creating a unique and exciting plot.
One way is through a charity event. BTS is often involved in charity work, and YN could be performing at a gymnastics - related charity event. They meet there and start interacting. Another way could be if YN is a back - up dancer for another K - pop group and during a big K - pop concert, BTS and YN cross paths.