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.
According to the story, a good listener should show empathy. That means trying to understand the feelings of the speaker. If someone is sad while talking, you can give a sympathetic look or a gentle touch on the arm to show you care. Also, don't interrupt. Let the person finish their thoughts before you start to talk. This gives them the respect they deserve and also helps you to fully understand what they are trying to say.
The story might suggest that respect is a big part of being a good listener. Respect in terms of not cutting in and allowing the speaker to have their say completely. Also, having an open mind is important. Don't judge what the person is saying right away, but listen with an open heart and mind.
It's about a radio host who gets involved with a story of a supposed abused child through letters. He becomes very invested in the boy's story, but things start to get murky as he tries to verify the truth.