Demon Slayer: Kimetsu no Yaiba's Hashira Training Arc just ended, serving as a prologue to the finale. There was some controversy about its pacing (specifically, that it presented a brief portion of the manga despite having relatively little source material), but I want to put that aside to talk about what I think is the most important moment of the season—highlighting the core aspect of the main villain, Muzan Kibutsuji.
In the final episode of the Hashira Training Arc, Muzan confronts the head of the Demon Slayer Corps, Ubuyashiki Kagaya, who is bedridden and not long for the world. The ageless Muzan taunts Ubuyashiki for his physical decline, only for Ubuyashiki to discuss Muzan's obsession with his own immortality. The Demon Slayer leader juxtaposes this obsession with the Demon Slayer Corps' driving force: while it may be composed of mortals, their collective will to defeat the demons remains. Conversely, the demons rely entirely on Muzan to continue to exist. If he dies, so do they.
There is an inherent opposition between the group structure of demon hunters and demons. Muzan has created a system where he alone holds all the cards, surpassing even the most tyrannical despot. And he not only sees his minions as property, but is unwilling to cede any degree of power to them that is not under his complete control. While Ubuyashiki's followers respect him for his compassion and determination, the demons cower in utter fear of Muzan because they are nothing without him. The legacy of the Demon Slayer Corps continues, and not simply through the birth of children. Instead, it is carried out primarily through teaching and nurturing the next generation to be better.
The difference between Ubuyashiki and Muzan comes down to selfishness. It's the boss who expects people to obey and beckon, it's the narcissistic parent figure who demands their children obey them just because, the political leader who passes laws to benefit themselves rather than their citizens. It's not necessarily that overthrowing Muzan would destroy the demons, but the man who set things up that way, mistaking his weakness for strength. Since we're waiting for the final trilogy to wrap up Demon Slayer, I'm interested to see how it all plays out.