Masterba Shion is a student who endulges in jerk-off competitions with his classmates. Forced to move out of town and change schools, Shion finds himself getting bullied by one of his schoolmates, Ginji Fujita, to relieve stress, Shion decides to ejaculate in the nearby river, accidentally fertilizing a salmon egg.

After 3 years, a salmon humanoid arises from that same river, seeking for his dad.