At the notoriously brutal Sparta Academy, the perverted faculty continues its reign of terror, subjecting students to humiliating punishments for the slightest infraction. The only hope for the student body remains the mysterious masked vigilante Kekko Kamen, who fights for justice while wearing nothing but a red mask, scarf, gloves, and boots. In Kekko Kamen 3, the stakes escalate significantly when the villainous principal known as Toenail of Satan unleashes his extended family to destroy his nude nemesis once and for all. This family of assassins consists of twisted parodies of other famous characters from creator Go Nagais manga universe, including figures resembling Devil Man and Cutey Honey, each a crazed killer with their own unique fighting style.

The story picks up with the continuing persecution of first-year student Mayumi Takahashi, whose good-natured but academically struggling disposition consistently lands her in the schools torture chamber as bait for the masked heroine. However, Kekko Kamen faces an unexpected complication when she finds herself falling in love, an emotional distraction that seriously hampers her usual aggressive and exhibitionist combat style. As she hesitates and second-guesses herself, the villains press their advantage, forcing the heroine to confront whether romance has made her too weak to protect Sparta Academys students. The narrative explores how personal feelings can become vulnerabilities for a warrior whose primary weapons have always been fearlessness and utter shamelessness.

The conflict builds toward a climactic confrontation that expands the mythology considerably. Rather than facing her enemies alone, Kekko Kamen receives backup in the form of an entire army of women dressed in her signature red mask and boots, leading to a finale that delivers an unprecedented gathering of the heroine. This Kekko Kamen Army sequence serves as the films centerpiece, offering a spectacle that embraces the franchises absurdist humor while providing a definitive answer to the villains assassination plot. Throughout the 95-minute runtime, director Yutaka Akiyama balances the series trademark sex comedy elements with a more plot-heavy structure, exploring themes of identity, vulnerability, and whether justice can still be served when a superheroes heart is no longer solely dedicated to the fight.