WARNING: The following contains spoilers for Demon Slayer: Kimetsu no Yaiba Season 2, Episode 13, "Layered Memories," now streaming on Funimation, Hulu and Crunchyroll.
If there's one thing Demon Slayer: Kimetsu no Yaiba wanted to make clear in Season 2, Episode 13, it's that Tanjiro and Nezuko have had it with demons. The Kamado siblings have suffered enough for several lifetimes at the hands of Muzan Kibutsuji's creations, and Daki, Upper-Six of the Twelve Kizuki, managed to push both of them over the edge. In a pair of spectacular and bloody battles, Tanjiro and Nezuko reached new heights of power, but the question is: how?
As it turns out, Daki has been toying with Tanjiro to an insulting degree up to this point. After summoning her belts from all over the city to reenter her body, Daki's speed and power both shot through the roof. Sporting a new hair color as well as more belts to slice'n'dice her enemies with, her excitement upon sensing a Hashira in the area resulted in the horrific destruction of an entire city block. The kid gloves with which she was handling Tanjiro are definitely off as she has gone full bloodthirsty demon, flexing her power as an Upper-Rank.
Tanjiro Picked Daki Apart with Quiet Fury
The scale of Daki's instant destruction goes far beyond anything Tanjiro had ever seen thus far in Demon Slayer. Furious at the senseless slaughter, the hero's eyes filled with blood as he, surprisingly, became eerily calm. Showing off speed and power several times greater than ever before, Tanjiro looked like a Hashira as he used cold calculation to outmaneuver Daki at every turn, cutting her and her belts to pieces with some seriously amped up Sun-Breathing. If this is the full power of the original Breathing Style, it's clear now why Muzan's cells inside Daki's body began trembling in the face of Tanjiro's wrath.
It's not clear what exactly happened to Tanjiro; his flaming katana was not only cutting Daki's belts like butter, but burning the demon in a way that hampered her ability to heal. If Tanjiro's newfound power had held out for just a moment longer, Daki definitely would have become the former Upper-Six. Once Tanjiro's surge hit its limit, he was too busy hacking up blood to continue the fight, which would have no doubt been the end of his life if Nezuko had not come to his rescue. Every time Tanjiro masters something, a new ability he can't handle destroys his body -- but if he learns to endure whatever happened to him while fighting Daki, he would surely be even stronger than the Hashira.
Nezuko Obliterated Daki with Blind Rage
Punting Daki's head right off her shoulders, Nezuko put herself between the Upper-Rank demon and her wounded brother, ready to take up the fight. Nezuko has had her fair share of scraps before, and while she's a powerful demon in her own right, she was no match for Daki and was quickly sliced to pieces. However, she regrew her missing limbs so quickly that Daki realized her regenerative abilities are on par with an Upper-Rank's. In a new, more demonic form, Nezuko picks up where she left off by rag dolling Daki once again. Both fortunately and unfortunately, demons can't kill each other, but hopefully Nezuko's new form will keep Daki occupied long enough for Tengen Uzui to come to the rescue.
So, what happened to the Kamado siblings that they both powered up tremendously in this fight? A memory of their deceased younger brother holds the answer. The boy once mentioned that even though Tanjiro and Nezuko are so kind, they scare him with how angry they can become. Tanjiro's rage at Daki's massacre maxed out his Sun-Breathing power, while seeing her brother so wounded forced Nezuko to remember her family's slaughter, causing her to lose control.
It turns out the eldest Kamado children are known for their tempers, and Daki managed to enrage them both. As Demon Slayer moves forward, two questions remain. Can Tanjiro recover from his newest injuries? And is this more demonic form a new power for Nezuko, or is it just the new her?