Demon King Dearvil deeply despised the magical beautiful girl warrior Fontaine, who stood in his way as he sought to conquer the town. Her power stemmed from a mysterious source known as the "sacred virgin's pure heart," and he believed that destroying this purity would allow him to achieve his goals. One day, his soldiers discovered that Fontaine was actually a high school girl named Yuna Murakawa. Dearvil plotted to corrupt her innocent heart and strip her of her power, using her younger brother, Takumi Murakawa, as a key pawn in his scheme. Forced to live together, Yuna gradually fell into Dearvil's trap, her rationality as Fontaine crumbling as she stepped into a forbidden world. Ultimately, this led to a tragic BAD END.