Tanjiro and the hashira failed. Muzan got ahold of Nezuko and ate her. He now had the ability to be in the sun, while giving his Uppermoons, Kokushibo, Douma, and Akaza the ability as well.

Humans were no longer safe, even during the day. An outbreak happened, demons went on a murder rampage. Humans were either getting killed, eaten, captured, or turned into a demon.

Many villages were destroyed, and the only option humans had was to go into hiding. Even the tiniest noise could attract a demon.