Best friends Karen and Mizuki are recruited by a familiar named Clio to become "Uteas," magical girls tasked with purifying dangerous magical beasts. However, they quickly discover that purifying a lust beast requires a shocking and erotic process of physical submission and impregnation. After experiencing the beast's overwhelming pleasure, the girls are left to contemplate whether they can handle the lewd demands of their new duty to save humanity.
After encountering a deceptive lust beast, Mizuki is lured into a trap of pleasure and corruption, eventually losing her humanity as she gives birth to new monsters. With Mizuki's soul corrupted and Grace reborn, the mysterious Clio reveals the true nature of their existence and initiates the sinister Utea Project.
Karen is devastated to discover that Mizuki is actually a lust beast and that the Utea Project was a plot to corrupt magical warriors by tainting their powers from the start. Through a seductive process of "purification," Mizuki manipulates Karen's emotions and desires, eventually convincing her to abandon her duty as a purifier. Karen ultimately succumbs to the pleasure and transforms into a lust beast, leaving the two girls as powerful catalysts to ensure the prosperity of the lust beast race.
Aspiring to follow in the footsteps of the magical girls who once saved them, Kikka and Tsubaki are lured into a "purification dimension" only to discover that the magical girls have actually become lust beasts. After succumbing to the corruption and transforming themselves, the two girls join the hunt for high-profile targets to convert them into beasts for their mysterious king.