Juuseiki Guilstein

A string of murders occurs in which 15-year-old boys kill their families. Iori Takigawa, a 15-year-old, frequently dreams of turning into a monster and murdering his family, with a girl always present in the sky. At school, he learns from Imazeki, son of the police commissioner, that the boys in the cases transform into monsters and attack their families. On his way home, Iori and his friend Kikuchi are attacked by delinquents. Kikuchi suddenly becomes a giant monster, defeats the attackers, and then turns on Iori.