Muzan Kibutsuji, the supreme demon king, was not one to be easily intimidated. He was feared by many, but there was one demon slayer who made him tremble in fear – Yoriichi Tsugikuni. Yoriichi Tsugikuni, the fierce demon slayer, was deemed the “most powerful demon slayer in history.” Saying his name is enough to give Muzan PTSD! So, what made Yoriichi so special? Why was he feared by even the most powerful of demons? Let’s delve into the reasons behind Muzan’s terror. But beware, spoilers lie ahead!

Muzan and Yoriichi’s first encounter
Yoriichi Tsugikuni is a man with a purpose. From the moment he laid eyes on Muzan, he knew that his destiny was to defeat him. Despite Muzan’s initial underestimation of Yoriichi, the demon slayer proved to be a formidable opponent.
Yoriichi had achieved a state of selflessness that many martial artists only aspire to. He has a unique red-colored nichirin sword and possesses the ability to see into the “transparent world” or the sixth sense, allowing him to view through a person or demon’s body. He could effortlessly slice through Muzan’s body with his very own “Sun Breathing” technique, the most powerful breathing style known to give no enemy a chance to escape, hindering his regenerative ability. This was a crucial factor in their first battle, as Muzan’s regenerative abilities had been a source of fear for many demon slayers in the past.

The first time Muzan and Yoriichi met, the demon king almost lost his life. Yoriichi had come close to defeating him, but Muzan was able to scatter his own body and flesh, making it difficult for the demon slayer to eradicate him completely. Yoriichi tried his best to slice off all of the remaining parts, but they were too small, allowing Muzan to recombine into his original form once again.
Despite Muzan’s immense power and position as the demon king, he was unable to overcome Yoriichi’s strength. This led Muzan to flee and constantly be on the run, becoming the prey even during the night. The fear that Yoriichi instilled in Muzan was so intense that it left him still haunted by the memory of their encounter.
Read more: 10 Interesting Facts About Muzan Kibutsuji in Demon Slayer

Kokushibo is no match to Yoriichi
Kokushibo or Michikatsu Tsukiguni, the major antagonist of the series, was a formidable opponent. Despite his position as Muzan’s most powerful demon, a brother of Yoriichi, and let’s not forget that he also possesses a unique breathing style called “breath of the moon,” he was still unable to defeat Yoriichi.
One starry night, a fight between brothers took place, with Yoriichi cutting Kokushibo even before he could draw his sword. This act of sheer strength and skill left Kokushibo seething with anger and jealousy. He couldn’t understand why his older brother was still stronger than him, even after turning into a demon with a breathing style.
Despite his best efforts, Kokushibo saw no opening in Yoriichi’s stance. Yoriichi, who was old then, was just as strong as he was in his prime. However, just as Yoriichi was about to deliver the final blow, the next attack never came. Yoriichi died a natural death from old age, standing on his feet, leaving Kokushibo to ponder the sheer power of his brother.

Yoriichi’s legacy continues to torment Muzan despite his death
Even after his death, Yoriichi Tsugikuni’s power remained unparalleled. In the manga, the wounds Yoriichi gave to Muzan still continued to burn his flesh for hundreds of years, serving as a constant reminder of the power that the demon slayer possessed.
The team defeated Muzan, thanks to Yoriichi’s breathing style teachings passed down from generation to generation of demon slayers. The demon slayers were able to harness Yoriichi’s techniques to become a formidable force against the demons, and their collective strength proved too much for Muzan to handle.
Yoriichi’s power was so great that even Muzan, the strongest demon himself, described him as a monster, not him. This highlights the magnitude of Yoriichi’s power and skill and the lasting impression he had on him.
Read more: What Are Nezuko’s Demon Powers So Far?