When Tanjiro discovers that there is a demon in Ogimoto House, he abandons his disguise as Sumi-chan and reports to Koinatsu Oiran, who is set to be married and will therefore be leaving her post.. He tells her that he’s been investigating a demonic presence in the Entertainment District. He bids her farewell and runs out into the darkness. Soon after, Daki’s signature obi (sash or belt) makes an ominous appearance in the Oiran’s chambers.

Out in the darkness, Tanjiro comes face to face with Daki, and can easily tell that she’s way stronger than he is. Revealing herself to be the Upper Sixth Ranked Demon of the Twelve Demon Moons, Daki takes great pleasure in steamrolling our protagonist. While he doesn’t get through it unscathed, Tanjiro survives many of Daki’s heaviest hits, and as the fight progresses, he goes into a kind of autopilot mode that has Daki struggling against him from time to time.

The brawl against Daki pushes Tanjiro beyond the limits he knew, but as it progresses, we’re let in to a potentially dangerous secret: Tanjiro is not at full health. He’s actually been suffering from a fever for the past few months, with his body temperature reaching a searing 38 degrees Celsius! He believes this to be optimal for his fighting, and feels completely healthy, so with that in mind, Tanjiro unleashes several unseen Hinokami moves, slashing through Daki’s tough obi like butter.

He moves with a never-before-seen precision and veracity, overwhelming Daki even after she reabsorbs her obi and assumes her final form. Tanjiro’s body is clearly reaching its limit, as Daki lands more devastating blows, and as he pushes his body beyond anything we’ve seen thus far. The blood vessels in his eyes dilate and burst, giving him a feral, bloodthirsty appearance, and his frazzled hair and intense focus add greatly to the idea Tanjiro possesses the sufficient level of insanity required of a high-ranking member of the Demon Slayer Corps. He regulates his breathing, maintaining a level of Total Concentration that even makes his perception sharper. At this point, Tanjiro isn’t even breathing anymore.

The fever, combined with the intense focus brought on by his genetics, training, Total Concentration, and complete control over breathing, allow him to perform Hinokami moves we have not yet seen, tapping into the memory embedded in his very DNA and childhood memories, to pull off incredible techniques that even sear the parts of Daki that come into contact with Tanjiro’s sword! This clearly isn’t just Flame, but a call back to his father’s Sun Breathing heritage.

Daki, astounded by Tanjiro’s ever-improving abilities mid-combat, is bombarded by her own version of genetic memory: the blood of Kibutsuji Muzan within her reacting to the Sun Breather combat techniques Tanjiro performs. This adds another layer of mystery surrounding Muzan and the Kamado family, as well as the level of Tanjiro’s performance in this fight—is he comparable to someone who struck fear into the very DNA of Kibutsuji Muzan? As Tanjiro pushes himself to the limit, he sees visions of his little sister begging him to breathe. That first breath breaks Tanjiro’s focus and leaves him coughing and choking on the rooftop before Daki, whom he was seconds away from decapitating.

Winded by his overexertion in combat, Tanjiro is vulnerable before Daki, who is still frozen in shock. She soon snaps out of it to deliver a finishing blow upon Tanjiro, but Nezuko appears out of nowhere to deliver a kick that scatters Daki’s head across the area, but it doesn’t kill her. Angered by Nezuko’s attack, Daki delivers a series of powerful blows upon Nezuko, leaving her bloodied and beaten. Nezuko’s on a mission, though, as she goes into full “Protect Tanjiro” mode, revealing a form we’ve never seen before.

Nezuko’s body is decorated by a vine-line similar to Daki’s face flowers or Akaza’s basketball look, and she has a horn growing out of the right side of her forehead. Her overall size increases, her bamboo gag falls away, revealing sharp fangs and an intimidating scowl. Nezuko means business in this fight, and her new appearance sends Daki into a fearful realization: Kamado Nezuko isn’t just a powerful demon, she’s at least at the level of an Upper Ranked Demon of Kibutsuji Muzan’s Twelve Demon Moons! There was already evidence of this—her Blood Demon Art. Daki’s appraisal comes at a time where we, the audience, have been reckoning with the true abilities of the Kamado siblings ever since Rengoku Shinjuurou, the father of Kyojuurou, made the observation that Tanjiro wears the mark of the Sun Breathers.

In her new form, Nezuko totally devastates Daki, kicking her bloody, and stomping her with a vengeance. Nezuko has totally lost her reason with this transformation, and the visual cues for this are her more feral appearance and evil smirk as she stomps Daki out like winemakers did grapes in the olden days. Nezuko’s regeneration abilities are several times more effective than Daki’s, and even having her head and limbs severed doesn’t stop the onslaught Nezuko unleashes upon her. Passed out from overexertion, Tanjiro sees visions of a younger sibling begging him to wake up and tend to Nezuko who, at this rate, “will cease to be herself”. Nezuko’s cruelty towards Daki intensifies when, after Daki uses her obi to slash Nezuko to literal pieces, Nezuko’s blood splatters on the unsuspecting demon. In the next instant, Daki bursts into flames, courtesy of Nezuko’s Blood Demon Art. The fight ends up destroying several buildings and some civilians get wrapped up in the chaos. With Daki beaten to a pulp, feral Nezuko’s attention turns to an injured civilian. Before Nezuko’s lunge reaches her target, Tanjiro manages to hold her back using his sheathed sword as a gag.

Away from the Kamado siblings’ boss battle against Daki, Inosuke has found the demon’s core where all the victims are held fast in her obi and worked on cutting them free, finding Uzui’s wives among the victims. Daki would imprison her victims in the very fabric of her obi to eat them later. Daki’s obi is sentient and reflects some of her more negative traits like abrasiveness, overt hostility, and a superiority complex. In this lair, Inosuke and Zenitsu are met by Uzui, who arrives just as Obi Daki is about to skewer one of his wives. We get a fun reunion and introduction to Uzui’s wives, as well as an allusion to the true nature of Daki’s powers.

Something really unexpected happens when Daki, angered by Nezuko’s assault, decides to make use of the opening left by Nezuko’s rampaging demon hunger—she is swiftly beheaded by Uzui, but she doesn’t seem to be withering away. Broken by her defeat and frustrated by Uzui’s taunting, Daki weeps before calling out to her big brother, who emerges from her back in a grotesque display reminiscent of Yu Yu Hakusho’s own demon sibling pair, the Toguro Brothers. It would appear that the idea of Daki’s obi being a separate consciousness but the same being was merely a kind of decoy for the real deal: Daki’s Upper Sixth Rank comes as a package deal with her older brother’s strength! They’re actually a duo-demon, one demon formed from two, and with that, Uzui has a bit of a problem on his hands!