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Despite having minimal screen time in Demon Slayer to now, Muzan Kibutsuji manages to capture and hold viewer’s attention whenever he’s on screen or mentioned. This often results in fans asking whether Muzan was a Demon Slayer, or what happened to his family after he became the demon progenitor.
While anime viewers have not been introduced yet, manga fans have questioned whether the Upper Moon One demon is stronger than Muzan. The key difference between their Yoriichi encounters makes an easy answer to the question. Anime fans may think it silly that there’s a demon who could give Muzan a run for his money, but one does exist.
WARNING: HEAVY DEMON SLAYER ANIME AND MANGA SPOILERS BELOW
The facts
The common denominator when comparing Muzan and Kokushibo (Upper Moon One) is their shared experiences with Yoriichi Tsugikuni. Both have near-death experiences with the widely hailed greatest Demon Slayer of all time, and both receive a similar attack.
Against Muzan Kibutsuji, Yoriichi was able to behead Muzan and attack all 12 brains and hearts in one fell swoop. Yoriichi makes it clear that Muzan’s head wasn’t attached, but rather Muzan was holding it on top of his neck in hopes of regeneration. That regeneration didn’t come.
Muzan was also able to escape after this beheading assault, resulting in roughly 300 pieces combining to the size of a human head. Muzan thus regenerated from that lump of flesh back into a full body. The important note to make here is that Muzan was able to survive beheading without any problem; this is confirmed by Tamayo’s lamenting of this ability.
Against Kokushibo, Yoriichi was able to nearly behead the Upper Rank One in one swing. Kokushibo makes note after the fact that Yoriichi’s speed and power was the same as in his prime. Thanks to an official colored panel, we also know Yoriichi used his red Nichirin Blade against Kokushibo as he did Muzan.
Essentially, everything was the same here except for two major differences. Against Muzan, Yoriichi uses Sun Breathing and the style’s Thirteenth Form to behead Muzan and target all 12 hearts and brains.
Against Kokushibo, Yoriichi merely swings his sword without visibly using any breathing techniques. The second major difference is Kokushibo’s age, specifically his being on death's door when facing Kokushibo.
The argument
While both of Yoriichi’s fights are some of the most influential in Demon Slayer, the greatest Demon Slayer of all time was unfortunately unable to kill both Muzan and Kokushibo. While Muzan legitimately beat Yoriichi by escaping and regenerating, it’s hard to argue Kokushibo truly won against his twin brother.
When facing Kokushibo, the greatest Demon Slayer of all time was in the final moments of his life. After making a cut too shallow to behead Kokushibo, the Upper Rank One demon forfeited his life, saying he was sure Yoriichi’s second blow would kill him. Fortunately for him, Yoriichi died standing up in the recovery from his first attack on Kokushibo.
Muzan was also nearly defeated, but the key difference is Muzan escaped from a living Yoriichi. Kokushibo quite literally needed Yoriichi to die in order to walk away from that battle alive. Had Yoriichi had mere moments more of life, the Upper Rank One slot would be occupied by someone else when Demon Slayer takes place.
The verdict
The answer to whether Upper Moon One is stronger than Muzan in Demon Slayer is quite clear; Kokushibo is not stronger than Muzan Kibutsuji. The main piece of evidence here is that Muzan was able to escape a living Yoriichi, whereas Kokushibo needed death’s assistance to prevail.
Both fights are very similar in how they unfold versus the best Demon Slayer of all time, but the one key difference here is how they end. While Yoriichi did make quick work of Muzan, the progenitor of demons was still able to beat Yoriichi in the end by escaping via his own power.
Yet Kokushibo was much more fortunate; Kokushibo simply needed to wait for Yoriichi to die. While Kokushibo couldn’t have known the greatest Demon Slayer would die in that moment, it still helped him survive in the end.
