The Infinity Castle Arc in Demon Slayer is one of the final and most intense parts of the story. After the Upper Moon 5 demon is defeated, Muzan’s hidden base — the Infinity Castle — is revealed. The Demon Slayer Corps is pulled into the castle, where they are separated and forced to fight the strongest demons, including the Upper Moons. The castle constantly shifts, making battles more chaotic. This arc is known for its epic fights, major character sacrifices, and the beginning of the final war against Muzan, showcasing incredible animation.
The personal lair of the Demon King, Muzan Kibutsuji, in Koyoharu Gotouge’s Demon Slayer, the Infinity Castle is a never ending fortress created by the Blood Demon Art of Nakime, a demon in Muzan’s employ.
The animation in this arc enhances the emotional impact of the story, making every battle feel more intense
Manifesting as a labyrinthine series of rooms, halls, platforms, corridors, and stairs, the space exists beyond the normal confines of space and time. Whenever he summons meetings among his closest subordinates, i.e., the Upper Ranks of the Twelve Kizuki, Muzan tends to call them to the Infinity Castle. But whereas the Upper Ranks are quite familiar with the presence of such a realm and how to navigate its breadth, the Lower Ranks know very little about it and were completely perplexed when called there following the death of Lower Rank Five demon Rui.
Later, making an appearance in Demon Slayer just before the Swordsmith Village Arc, the Infinity Castle was where the Upper Ranks had a meeting. The meeting was called by Muzan to speak about the defeat of Upper Rank Six demons Daki and Gyutaro, who were defeated by Tanjiro, Inosuke, Zenitsu, and the Sound Hashira Tengen Uzui at the conclusion of the Entertainment District Arc.
In contrast to the Lower Ranks, the most powerful of Muzan’s subordinates appeared well accustomed to the Infinity Castle, even though they had not been invited there for more than a century.
Some of the Upper Ranks even have personal rooms within the castle to call their own, as is the case with Kokushibo, who was quietly kneeling in a private area, well away from the central meeting area, after arriving at the location well ahead of everyone else. While Muzan does not occupy all of his time within the Infinity Castle, it remains his central hub of operations and functional home.
Inside Nakime’s Domain
Endless in scope at first glance, the Infinity Castle appears to have a mind of its own, as supported by the fact that its halls, chambers, and corridors seem to be shifting constantly. This condition of change occasionally occurs in random sequence, but it is subject to manipulation as needed on the whim of Nakime, who initially created the extra-dimensional world using the power of her Blood Demon Art.
Nakime has complete freedom to change the structure, volume, and spatial relationships between various parts of the castle to suit her needs, doing so via her biwa. Though not a lot has been seen of her personality and real nature in the anime yet, it is quite certain that she feels an extreme dedication towards Muzan and is devoted to him to an extreme, as she has permitted him to make the Infinity Castle his personal den.
Nakime is also able to change the location and position of any demon or person within the Infinity Castle according to her wish, doing so by playing her biwa. She is able to also change and close up pathways or open new ones at whim, providing her with an omnipotence within the realm that is similar to the strength of a god. One of the most striking aspects of the nature of the castle is the fact that there is no single source of gravity since residents can walk on virtually any surface with any inclination — even on the ceiling and walls in some places, or on inverted floors and staircases.
It is also possible to move in physically impossible directions all over the castle, which is only one of the numerous reasons Muzan chose it as his stronghold.
Demon King’s Stronghold
Muzan punishing his subordinate Muzan, the Infinity Castle is the only refuge place to which any member of the Demon Slayer Corps cannot reach, a haven accessible only to him and Nakime. He is able to go in and out of the area at will, and teleport Nakime to transport him between places around the castle, which he does with dramatic flair when speaking to the Twelve Kizuki.
When at the first Lower Ranks meeting, where Muzan essentially killed them all except Enmu, he teleported from a place far in the depths of the castle to a balcony that opens outwards thanks to Nakime. At the time of the Upper Rank meeting, Muzan teleported Gyokko’s severed head from the venue for the meeting to the palm of his hand, and then sent it back in an instant.
In calling and returning Muzan’s underlings, Nakime teleports them instantly from where they are at the moment to inside the Infinity Castle, suggesting that she is capable of capturing anyone as long as she knows where they are. Muzan was also able to use this in the final battle against the Hashira and the whole of the Demon Slayer Corps. Most of this fight occurred within the Infinity Castle, as hordes of demons who were upgraded by Muzan to the strength of a Lower Rank, were under his command to serve as minions to flood the Demon Slayer Corps’ troops.
A Labyrinth Of Horrors
Lower Moons Infinity Castle Demon Slayer
Randomly changing its spatial order at any given moment, with no clear logic in this unstable state, the infinity Castle is a three-dimensional maze-like structure where every inhabitant apart from Muzan and Nakime have to completely surrender to their lack of control. The immensity of the realm and disregard for the conventional rules of physics permits it to contain impossible structures, which Nakime can build and destroy at will.
From hundreds of levels of halls and passageways, to giant indoor gardens and voids so deep that they go far beyond what a real castle could accommodate. All this was laid bare when Akaza, the Upper Rank Three demon of Twelve Kizuki, tumbled through the castle grounds to the conjunction of the Upper Moons.
In essence, it is one of the strongest Blood Demon Arts depicted in the series, well beyond any other skill involved in handling space manipulation in Demon Slayer. The enormity of the Infinity Castle was showcased in all its glory at the start of the Swordsmith Village Arc opening episode, giving us a hint of what to expect when the manga’s last arcs are brought to life by Ufotable on-screen.
In the last fight, the Infinity Castle was a significant advantage to Muzan when fighting against the collective might of the Demon Slayer Corps, serving as a final desperate escape for him when things looked bleak. With the level of animation that has been witnessed at every step of the anime so far, it is certainly safe to assume that they will be able to do justice to this enigmatic, enthralling space, taking the visual experience of moving through it to even more unprecedented heights than ever before.
The Infinity Castle is the secret, ever-shifting stronghold of Muzan Kibutsuji, the Demon King in Demon Slayer. Created by the biwa-playing demon Nakime using her powerful Blood Demon Art, this castle exists in a completely different dimension — beyond time, space, and logic.
The castle first appears after the death of Lower Rank Five, Rui, when Muzan summons a meeting of the remaining Lower Moons. This shocking moment sets the tone for how dangerous the place is — Muzan kills nearly all of them, leaving only Enmu alive. This moment introduces fans to the terrifying control Muzan has over his demons, and how the Infinity Castle serves as both a throne room and a prison.
The structure itself is not just big — it’s endless. With floating platforms, twisting staircases, walls you can walk on, and gravity-defying rooms, the entire space feels like a nightmare brought to life. What’s more dangerous is that Nakime controls everything inside it. With just a note from her biwa, she can teleport demons or humans, move walls, open or close pathways, and change the castle’s layout instantly. She’s like a god inside this realm.
The Upper Moons are familiar with the castle — some even have their own rooms inside it, like Kokushibo, who meditates in a private chamber. But for the Lower Moons and intruders, it’s a disorienting death trap. They can’t predict or control anything, making escape almost impossible.
The castle plays a massive role during the Final Battle. Muzan uses it to teleport the entire Demon Slayer Corps inside, turning it into a deadly battlefield filled with traps, surprise demon attacks, and collapsing architecture. It gives Muzan a huge strategic advantage — but also becomes the place where his reign truly begins to fall apart.
Visually and symbolically, the Infinity Castle represents chaos and fear — a perfect reflection of Muzan himself. It’s not just a place. It’s a living, breathing horror — a fortress that moves, hides, and fights back.
With the anime’s final arcs approaching, fans are eagerly waiting for Ufotable’s animation of the Infinity Castle battles. Given their work on past arcs like Mugen Train and the Entertainment District, expectations are sky-high. The combination of storytelling, animation, and emotion will likely make the Infinity Castle one of the most unforgettable locations in anime history.
