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.
Another characteristic is that they can use fan service to enhance the mood or the character's personalities. In 'One Piece', Nami's outfits are sometimes a bit revealing, which can be seen as a form of fan service. But within the context of the story, it also shows her confident and sometimes cheeky personality. The overall story of the Straw Hat Pirates' adventures, their quests for treasure, and their battles against powerful enemies is so vast and engaging that the fan service becomes just one aspect among many that make the anime great.
'Food Wars! Shokugeki no Soma' also fits. The story is about a young chef named Soma trying to prove himself in a highly competitive culinary school. There is fan service in the form of the characters' over - the - top reactions to delicious food, which are sometimes depicted in a rather 'ecstatic' way. But the main focus remains on the amazing cooking battles and Soma's journey to become the best chef.