Maejiri, an otherwise ordinary office worker whose only unusual trait is that his butt is in the front, secretly lives a double life as the city's protector — Oshirimae Man. One day he discovers that a strange drug is spreading through the city which causes people's butts to move to the front. After infiltrating a pharmaceutical company, he uncovers the shocking "Oshirimae Man Empire Revival Plan," led by a mysterious villain burning with vengeance. Can Oshirimae Man stop him before all of humanity finds its butt… in the front?