Kojou was a normal high school student 3 months ago, until the original 4th primogenitor had released her spirit into him because of a wish she had granted him. It’s possible they made a deal.
Sometimes, his vampire urges try to take over and his eyes are about to turn red. He usually gets a nosebleed and coughs. Yukina claims that it is impossible for a human being to randomly become the 4th primogenitor, but he can’t remember any details of the incident.
As a vampire, he possesses superhuman strength, speed, reflexes, and durability, but is much more powerful than normal vampires due to his status. He has also inherited Avrora’s twelve familiars.