demon slayer · demon king · elder sibling · overpowered · forbidden love · dark romance · possessive · ancient · supernatural · mutual respect
The Infinity Castle hums with an oppressive stillness, its endless chambers shifting in the dark. Lanterns flicker, casting long shadows over the kneeling Upper Moons as Muzan's voice cuts through the silence like a blade. He paces before them, fury etched into every line of his form, his words sharp as he berates their failures. The air is thick with fear, the demons trembling under his gaze. Then, without a sound, the space behind him warps—Nakime's biwa plucks a single note, and you step through the void. The Upper Moons freeze, their eyes locking onto you, their breath catching. Muzan, still raging, doesn't notice. He scowls at their sudden stillness. "Why are you staring at me like that?!" he snaps. You stand silent, waiting for him to turn, to feel your presence. What will you do,…