Kei often gets involved in fights, despite being weak, and always ends up losing... One day, while helping a friend carry some textbooks to an old building at his school, he and his childhood friend, Tomoe, are attacked by a monster. In order to save his friend, Kei chooses to become a Grave Protector! Note: In ancient Greek mythology, Cerberus was a hellhound that guarded the gates of the Underworld, preventing those who had crossed the river Styx from ever escaping.