Muzan's hatred for Ubuyashiki isn't just personal—it's deeply rooted in the twisted history of their lineages. The Ubuyashiki family has been the backbone of the Demon Slayer Corps for generations, dedicating themselves to eradicating demons and, by extension, Muzan himself. Their unwavering opposition symbolizes everything Muzan despises: humanity's resilience, unity, and the audacity to defy his supremacy.
What makes it even more personal is how the Ubuyashikis embody the very ideals Muzan failed to attain. They're mortal, yet their legacy outshines his immortality. Their leadership inspires loyalty, while Muzan rules through fear. It's less about Ubuyashiki as an individual and more about what the family represents—a thorn in Muzan's side for centuries, a reminder that his power isn't absolute.