After slaughtering his entire family, Duke Sateriasis Venomania contemplates suicide until a enigmatic figure named IR intervenes. To change his destiny and win the love of his former tormentors, he accepts a demon's pact by impaling himself with a mystical katana. Gifted with the ability to enchant any woman, he indulges in creating a harem to alleviate his growing madness. However, a reunion with his childhood friend, Gumina Glassred, rekindles old wounds, leading him to ensnare her in his entourage for vengeance. As his demonic powers erode his humanity, his insatiable appetite drives him closer to becoming a demon himself. Amid his descent, adversaries emerge, ready to confront the monstrous fate he embraces.