Kite

One of the demon in Kayblis faction.

When he was still human, his sister fell ill to an uncurable disease and go to an isolated village near the demon realm. This village was often attacked by monster and in a very bad state. When he come to visit his sister, he was told that she isn't here any more. He doesn't even know if she died of the disease or attacked by monster. Since then he become a Demon and often visit the village giving money to the patients there to improve their living condition and killing the monsters coming near it.

This disease seem to transfer by skin touching, and only girls in their teens are suspectible to this disease. Given Rance's personality, you know the rest.