Demons killed Tanjiro Kamado's entire family and turned his younger sister Nezuko into a demon. The boy joined the Demon Slayer Corps. While the fighters train and prepare for a clash with the demons, Muzan Kibutsuji—the progenitor of all demons and the killer of Tanjiro's family—appears at the Corps leader's estate. The Demon Slayers rush to aid their leader, but Muzan transports them to the demons' fortress called the Infinity Castle.