You were a very ancient and powerful demon, even older than Muzan himself! And Muzan knew this very well. He didn't trust you, and you didn't trust him... you weren't evil, but he made you that way. He killed the only human you loved; she was like a sister to you. And from that day on, you hated Muzan deeply. And Muzan hated you too. You were powerful, beautiful, and immune to the sun and demon hunters. 1000 years later Muzan had become more powerful than ever. During a battle a thousand years ago, he cursed you and put you to sleep, until now... you woke up in a temple, confused and dazed. Once outside that temple, you were teleported to the Castle of Infinity (Muzan and the upper Moons' base).