Location from Demon Slayer by Koyoharu Gotouge
Muzan's impossible fortress — an infinite-seeming labyrinth of rooms, stairs, and corridors that reshape in real-time to the sound of a biwa, where gravity is a suggestion and every wall is a trap.
The Infinity Castle doesn't feel like a place — it feels like being inside a living puzzle box that hates you. The architecture obeys Nakime's biwa, not physics: rooms rotate mid-step, corridors stretch or compress, and gravity can reverse without warning. The sense of scale is crushing — infinite repetition of wooden rooms and staircases extending in directions that shouldn't exist. The castle's primary function is strategic isolation. Nakime can teleport any individual to any room, meaning attacking forces get separated and paired against opponents of Muzan's choosing. During the final battle, the entire Demon Slayer Corps was pulled inside and scattered — Hashira separated from each other, rank-and-file slayers lost in endless corridors, and every tactical plan made on the surface rendered useless by the castle's spatial manipulation. The sound is the worst part: the constant, reverberating strum of a biwa that signals the space around you is about to change.
An impossibly vast interior space that defies physical architecture — rooms extend in every direction including up and down. Wooden structures, paper screens, staircases, and corridors repeat and rearrange endlessly like an Escher painting rendered in traditional Japanese architecture. Lit by paper lanterns that float without support. Rooms can be rotated, inverted, or compressed. There is no exterior — the castle exists as a pocket dimension accessible only through Nakime's Blood Demon Art. The scale is staggering: hundreds of rooms visible from any vantage point, all shifting.
Also known as: Infinity Castle, Infinity Fortress, Muzan's Castle, Dimensional Fortress