A terrible creature has been plaguing the community: a man with a fishbowl for a head. When he attacks someone, the goldfish leaps out of his bowl and drinks their blood. The victim is irreversibly transformed into a goldfish! This terrible crime has happened to high-schooler Kousuke’s little sister. With no other option, he takes care of his goldfish-sister as best he can.

Sometimes, the day after it rains, a tall man with a fishbowl instead of a head stalks through the streets assaulting people, drinking their blood, and then turning them into a goldfish. The townspeople are completely defenseless to his attacks, and must rely on blood divers, members of a vigilante group who jump into a victim’s body and stop the transformation, to keep this predator at bay. Ringo is one such blood diver who patrols the town with nothing but a plastic pistol and goldfish scoop, but she’s extremely inexperienced. Can the girl stop the fishy menace that’s terrorizing the town?!