Himejima, the Stone Hashira, and Shinazugawa, the Wind Hashira, face Kokushibo, the 1st Upper Moon, in a merciless battle. But despite the appearance of the Demon Slayer Mark, the two Hashira are only retreating against Kokushibo's overwhelming power. Seeing his brother in trouble, Genya swallows a piece of the 1st Upper Moon's flesh. Will his desperate act be enough to secure their victory?