Muzan Kibutsuji notes he is well aware that living creatures are able to tap into reserves of strength unbeknownst to them to escape death and looks on to see Tanjiro Kamado doing the same in his attempt to connect all twelve Forms of the Sun Breathing. He sees that Tanjiro has turned his blade bright red as well, just as the other Hashira had but is unconcerned as he says that the young Demon Slayer's attacks are nowhere near as powerful as those of Yoriichi Tsugikuni.
As the young Demon Slayer connects the Sun Breathing: Dragon Sun Halo Head Dance and Fire Wheel, he successfully manages to connect six of the Forms, however, he notes that Muzan's organs keep moving within his body and that the Demon's attacks prevent him from attacking his torso. Beginning to feel fatigued, Tanjiro heaves and slows down but he keeps telling himself to focus on one second while connecting the Sun Breathing: Fake Rainbow and Burning Bones, Summer Sun.
Muzan notices Tanjiro's attacks begin to lose their accuracy and surmises that he will soon lose his red blade as well, saying that he is yet another swordsman who would never live up to Yoriichi nor reproduce the terrifying technique the old swordsman had used against him.
Launching another attack towards Tanjiro, Muzan manages to connect and knock the boy back. Tanjiro coughs up blood as Muzan whips at him again, barely managing to evade it. Swiftly regaining his footing, Tanjiro resumes his task of connecting together all the forms of Sun Breathing. This puzzles Muzan as he wonders why he is struggling so much against one weak and wounded human being, who is growing weaker by the second.
Deducing that he himself is also growing slower as a one-on-one fight would have never lasted so long, Muzan suspects it is an aftereffect of the antidote injected into him by Tamayo. Resolving to ask her himself as he had absorbed her cells, Muzan seeks out her remaining presence in his subconscious.
Finding the remnants of the Demon within him as a severed head, Muzan holds it in his palm and asks her what she had done as he believed the drug only made Demons human again. Tamayo's head reaffirms this, but she smiles evilly and says that she won't tell him what else it does, as that would be something his multiple brains should figure out.
Enraged, Muzan crushes the remnants of Tamayo's head with his hand and tries an alternative method to figure out what had been done to him by reading the memories lying in her remaining cells. Delving through her memories, Muzan finds one of her in her lab with Yushiro and Shinobu Kocho. Recognizing Shinobu as the poison user who had fought Doma, Muzan watches as she suggested that they mix in two poisons instead of one under the assumption that he could withstand one of them, with the first poison being the antidote to turn Demons into humans and the second one being an aging potion Tamayo had concocted to make its victims older by 50 years every minute.
Suddenly realising that he had been struggling against the Hashira and Tanjiro because his body had been diverting strength to combat his aging, Muzan attempts to calculate how much he had aged. Noting that it had been almost five hours since Tamayo had injected him with the drug and that the aging potion had only begun to take effect three hours ago, Muzan is shocked as he realizes he had aged by 9,000 years over the whole battle. Recognizing he should have noticed this earlier when the color had not returned to his hair, Muzan jerks his head to the side as he hears a Kasugaigarasu announce that there are 59 minutes till dawn.
Tanjiro keeps continuing by using the Sun Breathing: Solar Heat Haze, Beneficent Radiance, Clear Blue Sky, Fire Wheel, Raging Sun and Flame Dance. Yelling at Tanjiro to stop jumping around, Muzan attempts to attack the young Demon Slayer again with renewed ferocity, but Tanjiro dodges his attack with the Sun Breathing: Fake Rainbow, and follows that up with Dance, Setting Sun Transformation, Burning Bones, Summer Sun, Dragon Sun Halo Head Dance and the Sunflower Thrust, with that he has successfully connected all 12 forms of the Sun Breathing. With renewed hope, he determines to keep doing so until daybreak, with even greater speed and accuracy.
Characters in Order of Appearance
- It is revealed that Tamayo's drug had an aging potion mixed in along with the Demon antidote.
- Due to this, Muzan has aged 9,000 years within the span of three hours.
- 59 minutes left until dawn.
- Tanjiro successfully manages to connect all twelve Forms of Sun Breathing, but he can't perform them fast enough to create the 13th Form.