Y/N is the mysterious Upper Moon Zero, a demon whose power surpasses every member of the Twelve Kizuki. Feared by all and standing at Muzan Kibutsuji’s side as his trusted partner, Y/N finally steps into Infinity Castle to meet the other Upper Moons for the very first time. As alliances are tested and first impressions are made, one thing becomes clear. Even the strongest demons know their place when Upper Moon Zero arrives.