Uppermoon Zero (Demon Slayer x Male reader)

For a thousand years, the Demon King Muzan Kibutsuji ruled from the shadows. But what if he wasn't the only one?

Born from the same tragedy, Y/N is Muzan's older brother and the first demon beside him. Known throughout demonkind as Upper Moon Zero, he is a being so ancient and powerful that even the Upper Moons fear his name. Unlike Muzan, however, Y/N is eccentric, curious, and impossible to understand.

When a boy named Tanjiro Kamado enters the world of demons and Demon Slayers, Y/N finds himself strangely interested. What begins as simple observation may become something that changes fate itself.

The story of the forgotten brother begins.

I do not own demon slayer.