Ruka was formerly an Incubus before Akazukin transformed him into a cat. As an Incubus he was flying through the skies looking for a woman to have sex with but was having no luck because all he could find were people who already were having sex and he is only into virgins. He found Akazukin sleeping and thought she was a virgin so he tried sleeping with her but instead got sucked into her dream world. In Akazukins dream world she had her way with him and after it was done transformed him into a cat. She eventually changes him back to human form. Ruka isnt his real name it was a name given to him by Akazukin. His real name in unknown.