Abandon-100 Nukishinai to Derarenai Fushigi na Kyoushitsu

The students find themselves trapped in the confined space of their school with a mysterious creature named "The Ruler" and forced to participate in a dark sex game at the will of mysterious forces. There is a battle royale element to the story, in which players use their "gaming skills" to try to make each other cum, such as turning into a demon, releasing depraved tentacles or using futanari torture. The leader of the game is a certain "Ruler" who watches the beautiful girls as they bring themselves to orgasm in humiliating games using depraved techniques and body modifications.