One of the things I really like about Mob Psycho 100 is that, although it involves a number of enemies/antagonists becoming the main character’s friends, this transition isn’t the result of the main character being aggressively cheerful and kind to them.
Instead, Mob is essentially neutral. He does have ethics and opinions, but it takes a long time storywise before he’s able to figure out what they are, much less voice them (which is another thing I love about the series, the theme of self-discovery). The antagonists’ redemption comes not so much from Mob pointing out that they’re wrong, but from Mob remaining neutral/passive in the face of their wrongness, which forces them to view their own actions from a more objective angle and realize on their own how wrong they are—generally spurred by guilt at what they’ve put the unresistant Mob through. It’s a really interesting approach to character development.
(Not to disparage stories where the main character does help redeem their antagonists by being aggressively cheerful and kind to them, though! I do enjoy those, I just wanted to point out the difference.)