When the demon Biwa player Nakime is manipulated by Yushiro, the Infinity Castle collapses, violently ejecting the combatants onto the dark streets of Tokyo. This begins the Sunrise Countdown Arc. The surviving fighters face a ticking clock: hold Muzan in place for approximately an hour and a half until daybreak, or watch him slip away into the shadows to regenerate indefinitely.
Muzan assumes a grotesque combat form, growing jagged mouths along his limbs and lashing out with barbed, whip-like tentacles capable of severing limbs in milliseconds. Tanjiro Kamado, poisoned and temporarily blinded in one eye, reconnects with ancestral memories to master the thirteenth form of Sun Breathing. By connecting all twelve standard forms into a continuous, unbroken loop, Tanjiro maintains non-stop offensive pressure against Muzan’s shifting internal anatomy, which features seven hearts and five brains that move freely through his torso.
As the battle wears on, the cumulative damage forces Muzan's old, unresolved trauma to the surface. The centuries-old scars carved into his flesh by Yoriichi Tsugikuni begin to burn and split open. The cellular decay caused by Tamayo's drug prevents Muzan from healing wounds inflicted hundreds of years in the past, giving Tanjiro and the Hashira bright red fault lines to target.
