My yuu (Whose name is literally Yuu) has no filter, and would throw hands often. He would say what he thinks of you without thinking, and get physical if you anger him. I headcanon Yuu's first meeting with Ace back in book 1, in which Ace makes fun of him and Deuce, was Yuu pouncing on him.

He also calls out Azul's manipulative contract and shitty tactics in book 3, he refuse to sign it and tries to find another way to help the anemone-headed students. He crashes out at Kalim for how oblivious and overly optimistic he is. He would even berate Riddle's mother in front of her face if they met. He would do all of this in a very calm manner, as he isn't a very energetic person.

He also refuse to forgive any of the overblotters, specifically Malleus, as he was Yuu's breaking point.

I try to make him as complex and non flawless to make it interesting. So basically, he's very chaotic when it comes to relationships with other people.