Muzan Kibutsuji is the main antagonist of Kimetsu no Yaiba. From the beginning, fans expected that Muzan would have a great backstory and the power to defend himself.
However, the final battle of the Infinity Castle arc was so predictable and linear that fans thought author Koyoharu Gotouge rushed to end the story of Kimetsu no Yaiba. Muzan's ending finally elevates villains like Naruto's Kaguya and One Piece's Kaido to the level of perfectly crafted villains.
Compare Muzan with Kaguya and Kaido
Before Kimetsu no Yaiba ended, the title of worst Shonen villain usually belonged to Kaguya and Kaido. Even in the eyes of the most ardent Naruto fans, all Kaguya has is the name chakra ancestor. She has no personality, no real backstory, no soul, just a boring villain.
For years, Madara Uchiha has been built up to be the final and most important villain of Naruto, and fans have been preparing for the story to end that way. Then, Kaguya Otsutsuki appears and immediately deposes Madara, becoming the final and most powerful villain in the series.
In the case of Kaido in One Piece, he was built up to be a fearsome villain on par with Doflamingo and Big Mom, but ended up looking like a bland, forgettable villain. immediately upon introduction.
Muzan is built in a similar way in Kimetsu no Yaiba. But since Muzan is the main villain of the entire series, unlike Kaguya and Kaido, the expectations for Muzan are higher.
Unfortunately, Gotouge turned Muzan into a mediocre villain, with no special powers, no backstory, made too many stupid mistakes for someone who was 1000 years old and died in the most pathetic way.
The ending of Kimetsu no Yaiba is not the worst in a Shonen manga
Kimetsu no Yaiba is not the anime series with the worst ending. Before disappearing, Muzan decided to pass on his will and emotions to Tanjiro, with the hope that he would become the strongest Demon King and destroy all demon-slaying swordsmen.
But luckily in the end, thanks to the efforts of his friends and his own strong will, Tanjiro overcame the darkness in his veins. He returned to being human without causing any damage. He ended Muzan's legacy by destroying him and refusing to accept his demonic self.
At the end of the story, a very long period of time passes, the main cast are reincarnated as their descendants, and demons disappear from the face of the earth.
Although this ending did not satisfy many people, at least Kimetsu no Yaiba showed the main battle with Muzan and answered all the questions the series raised at the beginning.
Compared to the ending of My Hero Academia or Jujutsu Kaisen, fans probably have to give more praise to the creator of Kimetsu no Yaiba.