Arisa, a schoolgirl working as a babysitter, is accosted by thugs from the Black Union. Suddenly, a mysterious masked naked warrior known as Harenchi Mask appears, defeating the thugs with nunchaku and powerful high kicks. The child held hostage joyfully cheers for Harenchi Mask, further embarrassing the modest hero. However, in that moment, the defeated thugs swear revenge and launch a new attack.