Kimetsu no Yaiba Season 1 Episode 7.
Tanjiro leaves Nezuko to protect Kazumi and the human girl from one of the three while he jumps inside their black hole to deal with the other two. Inside it is like a black swamp, but his Water Style shows its true power when underwater, letting him create a whirlpool that eviscerates the two. Nezuko physically beats back the remaining demon, who thinks she must have gotten a huge amount of blood from “him” to be so powerful. However, her lack of experience makes her attacks easy to read and the demon begins to regain the advantage when Tanjiro surfaces and disables him. Tanjiro orders the demon to tell him what he knows about Kibutsuji Muzan but the name terrifies the demon so much he attempts a suicidal attack rather than speak and is killed. Nezuko falls asleep and Tanjiro returns her to the box. Kazumi is in shock and shouts at Tanjiro when he tries to tell him to move on after his fiancee’s death, though realizes after Tanjiro gives him Satoko’s hairpin, smiling gently, that he’s been through something similar and apologizes, promising to take care of the girl. Tanjiro leaves, vowing to defeat Kibutsuji for the suffering he has caused. A Kasugai crow lands on his shoulder and directs him to Asakusa, Tokyo for his next mission, but Tanjiro finds Tokyo’s size and electricity overwhelming. While resting in a park he catches Kibutsuji’s scent and chases it down, leaving Nezuko behind in his hurry. He locates Kibutsuji as he walks down a busy street and is about to draw his sword when Tanjiro realizes he’s holding a girl who calls him “daddy.” A woman walks up and asks what’s going on and the girl in Kibutsuji’s arms calls her “mommy.” Tanjiro can smell the girl and woman are human – Kibutsuji is pretending to be one as well. To distract Tanjiro, Kibutsuji digs his fingernails into his palm to bloody them and casually slices the neck of a man passing by, turning him into a demon.