Kojō was a normal high school student 3 months prior to the beginning of the story, until becoming the 4th progenitor after his predecessor, Avrora Florestina inserted her spirit into his body as the result of a wish. He claims to remember nothing of the incident. When aroused, his blood lust takes over and the only way to satisfy it is to drink his own blood, usually from the nosebleeds he experiences. As a vampire, Kojō 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. Due to never having drank human blood, Kojō at first has no control over his powerful familiars, but after drinking an individual's blood, one familiar will acknowledge him as their master. By drinking the blood of others who have familiars, he is able to gain control over their familiar. By volume 9, he is able to control 6 of the familiars.