Kaien Kurosu (Cross) was always seen to have a rather cheerful personality. He's quite bubbly and friendly, and sometimes he wasn't aware of the personal space he invades but at the same time he was also quite a serious character when it comes down to business. The cheerful nature he had seemed to appear like a mask that hid most of his emotions. It was easier to play the role of the cheerful, go lucky Chairman of Cross Academy, a school that worked to create a co-existence between humans and vampires. He also had personality quirks that would sometimes be similar to just tearing up dramatically over being a poor parental figure for Yuuki in whom he adopted.

He enjoyed teasing his his children aka Yuuki and Zero, but of course Zero would never admit to even be part of Kaien's insane little family. Kaien still treated him as if he was his own child and same with Yuuki. He dotes on them and often liked to tease and mess with them. He also had his own serious moments with his children, such as trying to assist Zero when he was on the verge of becoming a vampire. Kaien helped him obtain the tattoo to somehow slow down the time that Zero would be turned into a vampire. In the end, he became a vampire and Kaien still tried to give him any assistance he could. Yuuki was the daughter of Juri Kuran, a friend of his he had met and been defeated by in the past. He did his best to protect Yuuki from the outside world and often pushed himself a little too much. Kaien also joked about Zero denying that they were family by saying that it broke his heart, but really he was happy to have these children with him even if he was just the 'adopted' parent. He also liked to cook strange food for both of his children and making them eat it.

He also had the tendency to go around and take pictures of his children when he got the chance, flashing cameras when he had time to do it. He displayed a sense of thoughtlessness be overriding and ignoring Zero's distaste for vampires. One of the strongest things he believed in was that vampires and humans could co-exist and he wanted to make it happen with his abilities, so that he could fulfill his promise to Juri. He didn't like to see humans and vampires at each other's necks or the crimes that were caused by vampires. He only hoped that the set up of Cross Academy would assist in making the life of vampires and humans a little easier and that not all vampires were bad. Humans shouldn't fear them and that was something that Zero would always disagree on. He often told things in half truths, because he wanted to protect his two adopted children, always leaving hints and implications here and there but never the whole truth. He also kept Yuuki's past a secret from both Yuuki and Zero.

He was proud and protective of his children and he would go through anything to protect them. With that set aside, Kaien Kurosu was also revealed to be a vampire hunter in the past. His personality then was a little different than his personality now. He was a lot colder and more serious, and this side of him is shown when he was protecting Cross Academy, or going into his fighting mode. His appearance and stature change depending on his actions as a Chairman or as a Hunter. Kaien had long abandoned his hunter status, but he was still a vampire hunter at heart. If he needed to take any form of action, he would not hesitate to do so. In his past, Kaien was known as the 'Vampire Without Fangs,' due to his inhuman strength and abilities. He was well known among the vampire hunters in the past.