WARNING: The following contains spoilers for Demon Slayer: Kimetsu no Yaiba Season 2, Episode 10, "What Are You?," now streaming on Funimation, Hulu, and Crunchyroll.
Things have just gotten real in Demon Slayer: Kimetsu no Yaiba's "Entertainment District" Arc. With the third episode's reveal that the demon Tengen Uzui is hunting is none other than Daki, Upper-Rank Six of the Twelve Kizuki, it seems Tanjiro, Inosuke, and Zenitsu are in for their toughest fight yet. Upper-Rank demons, Kibutsuji's ultimate creations, are the best of the best, and Daki has already made it abundantly clear she is not to be trifled with. With Daki's intelligence and power, the heroes definitely have their work cut out for them in Season 2.
Initially it seemed Tengen Uzui, the Sound Hashira, had only come to the Entertainment District because he'd realized a demon had moved in. However, it's now been revealed that Daki has been living in the city for several generations. Anyone who vanishes in the Entertainment District is quickly dismissed by those who notice their absence, making it the perfect place for a demon to feed. As for those whom Daki has no desire to consume, she makes their deaths look like suicides to keep suspicious eyes away from her.
The vast majority of Kibutsuji's demons in Demon Slayer, even some of the (now deceased) Lower-Ranks, are arrogant, impulsive and not overly intelligent. Daki, on the other hand, has not only found an ideal feeding ground, but she has perfected her methods to such an extent that she only occasionally must execute the rare person who has caught on to her. Changing her appearance every so often so no one becomes suspicious of her agelessness, Daki has shown a piercing intelligence that would be difficult enough to overcome even without her status as an Upper-Rank.
When Inosuke gets too close to her in Ogimoto House, despite his determination and hunting skills, she easily eludes him by moving about inside the walls. Daki swiftly escapes and finds her way to Kyogoku House before Inosuke could get anywhere near her. Having lived in the Entertainment District for centuries, Daki will be fighting the heroes in her home turf. Even if they do manage to get the upper hand against her, it's clear she knows the city better than they ever will, so if they intend to kill her, they'll have to do it quickly.
Unfortunately, killing an Upper-Rank demon is easier said than done in Demon Slayer, even for a Hashira. Worse, Daki has killed a total of seven Hashira during her time in the Entertainment District, meaning Tengen Uzui is just the latest one to try to stop her. Based on the fight between Kyojuro Rengoku and Akaza, showdowns between Hashira and Upper-Ranks are spectacular, intense battles, and Daki has apparently made a routine of disposing of these powerful swordsmen. It's not clear how powerful Tanjiro, Inosuke, and Zenitsu are in relation to Tengen, making it more than likely the Sound Hashira will have to do the lion's share of the work when the inevitable conflict with Daki begins.
Although Daki's threat level seems like it should be below Akaza's, as she is only Upper Six to his Upper Three, her Rank may be a misnomer. Two days before Tengen and the boys arrived, Daki was visited by Kibutsuji, her master and the Progenitor of Demons. During his visit, he treats her with polite respect, and though he sternly warns her not to get careless, he clearly holds her in much higher esteem than Akaza, whom he previously assaulted and berated. Considering he accused Akaza of having fallen and tells Daki that no demon is as strong as her, it could mean a well-deserved promotion is on the horizon for Upper-Rank Six.