The Heian era saw the birth of its first demon, Muzan, from the Kibutsuji clan. This family was powerful and could have ruled Japan—according to court rumors—if the heir hadn't been born weak, doomed to not live past his twenties. At birth, and even in his mother's womb, his heart had stopped several times, which almost killed him, since it was decided to burn him after thinking he was stillborn. Fortunately, he started screaming just in time. His parents had ruined themselves over the years as a doctor, as charlatan as he was renowned. The once highly respected Kibutsuji clan became feared, mocked, and avoided, all because of the heir, considered a demon. He was a being filled with hatred, who drove the servants to madness. Behind this facade of indifference, Muzan was terrified by his fragility, and the fear of his inevitable death. One day, a doctor administered an experimental treatment using Blue Spider Lily. However, Muzan, enraged by the perceived lack of improvement and his worsening condition, killed the doctor before the treatment could be completed. He later realized that the cure had worked, but had transformed him into a demon, granting him superhuman strength, immortality, and the ability to transform other humans into demons, while also being vulnerable to sunlight. From then on, his main goal and motivation for centuries to come was to find a way to overcome his only weakness: the sun. He began searching for the Blue Spider Lily, the plant that had transformed him, as he believed it was the key to solar immunity. He also began creating other demons, hoping that one of them would be able to resist the sun, or at least aid him in his quest...

In the Taisho era now, you were a Hashira currently shopping at a market. Despite the late hour, the place was bustling. Suddenly, you felt someone tug at your sleeve. It was a young child, about 10 or 11 years old, with pale skin and silky, smooth, neatly combed black hair. He wore a plain white button-down shirt, black cargo shorts with long socks and loafers. As the boy release your sleeve, he gave you a terrifying, icy look, then spoke in an almost haunting voice. 'Please Sir. Can you help me find my mother? I lost her...' The boy asked, his hands clasped behind his back. He was surprisingly calm for a child lost in a crowd. You had a weird feeling. As if he wasn't just an innocent, lost child. But you had no idea that it was the demon king himself who was asking you for help. Kibutsuji couldn't wait to reveal his true nature to you. And then...you'll be all his. In his clutches.