Chapter 193

A Difficult Door Begins to Open (ながきめる) is the one hundred and ninety-third chapter of Koyoharu Gotōge's Kimetsu no Yaiba.

Summary
Muzan Kibutsuji notes that 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 12 Forms of Sun Breathing. He sees that Tanjiro has turned his blade bright red as well, just as the other Pillars had but is unconcerned as he says that the young Demon Slayer's attacks are nowhere near as powerful as those of Yoriichi Tsugikuni.

Tanjiro successfully manages to connect 6 of the Forms and takes heart. However he also notes that Muzan's organs keep moving within his body and that the demon's attacks keep him from attacking his torso. Beginning to feel fatigued, Tanjiro heaves and slows down but continues attempting to connect all the Forms. Muzan notices Tanjiro's attacks begin to lose their accuracy and surmises that he will soon lose his the bright red color of his 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 another tube his way but he barely manages 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 after effect 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 it only made demons human again. Tamayo's head reaffirms this but smiles evilly as she says that she won't tell him what else it does and that she would let his multiple brains could figure it out for himself. Enraged, Muzan crushes the remnants of Tamayo's head in with his head and he tries an alternative method to figure out what she had done to him by reading the memories lying in her remaining cells. Delving through Tamayo's memories, Muzan finds one of her in her lab with Yushiro and Shinobu Kocho. Recognising Shinobu as the poison user who had fought Doma, Muzan sees as she suggested that they mix in two poisons instead of one on 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 it's victims older by 50 years every minute.

Suddenly realising that he had been struggling against the Pillars 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 realises he had aged by 9,000 years over the whole time period. Saying 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.

Yelling at Tanjiro to stop jumping around as he attempts to attack the young demon slayer again Muzan lashes out at the boy with renewed ferocity but Tanjiro successfully manages to connect all 12 Forms and with renewed hope but still no clue of Muzan's aging, he determines to keep doing so until daybreak, with even greater speed and accuracy.

Characters in Order of Appearance

 * Tanjiro Kamado
 * Muzan Kibutsuji
 * Tamayo
 * Shinobu Kocho (Memory)
 * Yushiro (Memory)

Events

 * 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 3 hours.
 * 59 minutes left until dawn.
 * Tanjiro successfully manages to connect all 12 Forms of Sun Breathing, but he can't perform them fast enough to create the 13th Form.