In Maruki’s case, people want validation, especially if you work in theoreticals. He was brought on as a councilor after Shiho’s attempted suicide. Then he saw Ren, Ryuji, and Ann magically reappear in the alleyway. Not long after, Kamoshida confessed and threatened suicide as has own atonement.

It doesn’t take a genius, just someone observant. The pieces kept coming together. The three volunteered to see him. Then they’re suddenly hanging out with someone not from Shujin but his mentor made a sudden confession. Then the student council president is seen hanging out with them. Then the gymnast goes from hurting to gaining a lot of self-confidence after being put under enormous pressure by the acting principle.