At Sparta Academy, an elite but deeply corrupt all-girls boarding school, the faculty has been replaced by sadistic perverts working for the evil organization known as the ManGriffon (MGF). The school's administration delights in handing out brutal S&M-style punishments for the most trivial offenses, using torture devices and humiliation to torment their students for their own gratification. The innocent and good-natured student Mayumi finds herself a primary target of this abuse when she tries out for the school's swim team, despite the fact that she cannot swim.

The MGF sends a new coach to take over the team, a grotesque frog monster who subjects the girls to twisted training regimens and whips them mercilessly for motivation. Mayumi in particular is put through increasingly horrific tortures, including a device called the Lung Capacity Amplifier, as the villains try to break her spirit. As the abuse escalates, the legendary naked crimefighter Kekko Kamen returns to Sparta Academy to right these wrongs. Wearing nothing but a red mask, red boots, and red gloves, and wielding her trusty nunchucks, this fearless heroine fights to protect the students from the perverted faculty.

Kekko Kamen's civilian identity is the one non-corrupt teacher at the school, though this secret is closely guarded. Her fighting style is as unconventional as her costume, featuring special attacks like the Muffication, a flying headscissor move that asphyxiates enemies with her radioactive private parts. Throughout the story, Kekko defends Mayumi and her classmates from the frog monster coach and his sidekick, who wears a frog costume for no explained reason. The narrative incorporates bizarre stylistic touches, including flashbacks presented as finger puppet shows, adding to the film's surreal tone.

As the conflict builds toward the finale at the school's swimming pool, Kekko must face an MGF that claims to be stronger and smarter than ever before. With the help of her alter ego, Mayumi finally learns to swim, and the two share an unexpected intimate moment before Kekko delivers the final blow to the villains. The story reaches its climax when Kekko defeats the MGF leader using her signature Muffication technique, saving the swim team and restoring a fragile peace to Sparta Academy, at least until the next threat emerges.