At the start he's very awkward with shion only really easing up when they enter the second train, one of the best parts of the game is how haru actually is suspicious about shion when he starts acting weird, even refusing to give him the knife/ the dialogue options letting you refuse him a lot more

Now the main points of character, he's weak and genuinely has low confidence but he does have the ability to hate, specifically and most tatsunami, now and his hatred for him makes a lot sense as much as I love his Char he def deserves a lot of that, the way he treated him at the start

Aoi even breaks up with him over how he's willing to hurt himself then ever hurt others, just before that he says "I am who I am." he calls himself weak like a lot like his confidence is so low it's actually sad sometimes funny, but it's really hammered in that he's a weakling

To start: a lot of people make him out to be growing bitter towards shion as he regains more of his memories and starts to doubt him even more which yes is a part of it, and we see that he's has a very weak mentality and generally doesn't have any confidence whatever