The story begins with the final moments of the battle between the Hero Sion's party and the Demon Lord Viraldzoard. Sion, wielding his unique skill, inflicts grievous wounds upon the Demon Lord, who, despite her beautiful appearance, is left battered and bleeding. Sion's companions, including the Holy Knight Tiana, the Great Saint Catherea, the Arch-Mage Euphemia, and the Bow Saint Ingrid, join the assault, driven by a cruel enjoyment of the Demon Lord's suffering rather than a sense of duty. Sion, however, feels pity for the Demon Lord, questioning the necessity of such brutal torment.
When the Demon Lord pleads for mercy, Sion's companions reveal their true, sadistic nature. Catherea then uses a forbidden ultimate technique, "Chaos Bind," to restrain Sion. Ingrid explains that this technique forces the Hero to self-destruct, using their life to break the Demon Lord's infinite regeneration and immortality. Euphemia then attacks Sion, followed by the others, as they explain that Sion will be hailed as a hero for sacrificing himself to save the world, while they will enjoy their lives. Sion dies in agony, betrayed by his comrades.
Sion awakens, miraculously alive and bandaged, to find himself in the presence of the Demon Lord Viraldzoard. She reveals that Sion's final act was not self-destruction but a desperate teleportation, saving them both. Viraldzoard, indebted to Sion, offers him refuge and healing within her castle, attended by skilled demon healers. Sion is bewildered by the Demon Lord's kindness and her assertion that demons desire only peace, a stark contrast to his ingrained belief in their evil nature. He expresses his gratitude, acknowledging the complex emotions he feels.
As Sion recovers, he discovers his physical abilities have been greatly enhanced. He can now summon his sacred sword, "Faria Leyda," with immense power, capable of splitting the earth with a mere swing. He also learns that his sacred sword is intrinsically linked to him, mirroring his condition. Viraldzoard, now preferring to be called "Villa," visits him, and they engage in increasingly friendly conversations. Villa reveals a surprisingly human side, becoming flustered when Sion uses her given name, and displaying a passion for coffee. Sion begins to question his preconceived notions about demons and their supposed evil.
Meanwhile, back in the human kingdom, Tiana and her companions report Sion's "heroic sacrifice" to the allied kings. They are celebrated as saviors and rewarded handsomely. However, Princess Maryann, who was in love with Sion, begins investigating ancient texts and suspects the truth: that Sion was sacrificed by his own party to defeat the Demon Lord. Tiana and her companions become increasingly anxious as Maryann's suspicions grow, especially when Catherea reveals that the Demon Lord might still be alive.
Sion and Villa venture out to quell a rampaging "Demon Dragon." During their journey, Villa displays a shy and endearing personality, further blurring the lines between enemy and ally for Sion. They discover the Demon Dragon, named Bash, is not inherently strong but possesses significant "growth potential," a trait unique to humans. Sion advises Bash to focus on training his "Dragon Fang Soldiers" to unlock his true strength.
Later, Villa expresses her desire for Sion to stay with them permanently, causing her to blush intensely. Sion finds himself increasingly drawn to her, realizing his feelings have shifted from animosity to something akin to affection. The narrative concludes with Sion contemplating the possibility that he and Villa, and perhaps humans and demons, do not need to fight.
