Kaoru's deal is that he's normal. He's SO normal. Everyone else is like "oooo I'm a vampire I'm doing 6d commercial domination chess I'm a child soldier" (and I love them for it) and Kaoru's problems are that he is grieving the loss of his mother and he fears he'll similarly lose his sister to an arranged marriage she'll be unhappy at and HE is gonna eventually lose his freedom to a life HE is going to be unhappy at, so he reacts be projecting a façade of not caring about anything and Dissociating and Crying About It, like Normal People Do.
But the thing is. Characters like Tomoya and Midori (both of which I like) have normalcy as a starting point, so it is used for comedy. Kaoru has Being Aggressively Normal as, like, the end result of his characterization. So the effect he has from Year 2 is that he's like, a walking zone of normalcy. Everyone who gets prolonged exposure to Kaoru remembers how to like, "process emotions" and "have a moral compass" when around him. You can be at the most ridiculous high-stakes Idol Mafia Spy Bullshit Story that Kaoru's very presence will force at least one other character to go "oh this is kinda messed up I should like, go to therapy and make amends with those I hurt today." He. Is so. Normal. And it's single-handedly keeping ES from falling apart.
