The tropical Seiren Island is a paradise for deviants: the infamous Pervert Law grants near-complete sexual freedom with almost no taboos or boundaries. With its various suggestive attractions, the Seirantou Health Organization (SHO) entices visitors while providing regular medical checks and contraceptive pills to ensure carefree enjoyment.
However, for high school student Junnosuke Tachibana, the island is far from ideal. Having recently moved there with his younger sister, Asane, he cannot stand the empty, loveless sexual acts. To make matters worse, Junnosuke's abstinence attracts unwanted attention—and those who defy the law face punishment. Junnosuke soon crosses paths with Nanase Katagiri, a notorious island seductress. Surprisingly, instead of forcing herself on him, she helps him flee from the SHO. Together, they discover a secret group that exists for a singular goal: to destroy the SHO. Now equipped with a way to resist the unjust rules, Junnosuke and other kindred spirits set out to crush the Pervert Law.