Kimetsu no Yaiba Season 1 Episode 4.
Urokodaki returns and, two years after Nezuko’s transformation, Tanjiro leaves for the Final Selection, the still sleeping Nezuko staying with Urokodaki. Before he leaves, he warns Tanjiro older demons who have eaten more develop new powers powers and gives him a fox mask with a spell to protect him. Tanjiro tells Urokodaki to say hello to Sabito and Makomo for him, startling Urokodaki, who wonders how he knows the names of those dead children. Upon reaching Mt.
Fujikasane, Tanjiro sees wisteria blooming and a number of other teenagers. The group is greeted by a pair of girls, who tell them many demons are imprisoned on the mountain, unable to leave because the wisteria they hate blooms year-round at the base. From this point on there is no wisteria and only those who survive for seven days will pass. Tanjiro is soon ambushed by two hungry demons but uses Water Style to kill them with a special “Nichirin sword” Urokodaki gave him. He detects a rotten smell and sees another applicant being chased by a massive demon. The applicant is caught but Tanjiro saves him. The demon asks Tanjiro for the year and is enraged when he learns he has been trapped here so long it has passed into another era. He curses Urokodaki for capturing him. The applicant can’t believe the demon is so old as there should only be young ones who have only killed two or three here, but this one has eaten at least fifty applicants.
The demon says Tanjiro will be the 14th student of Urokodaki he’s eaten, recognizing him by the style of mask. The demon recalls eating Sabito and Makomo and Tanjiro attack him, enraged. Sabito and Makomo’s ghosts sit on the slashed boulder, wondering if Tanjiro can defeat their killer. The applicant Tanjiro saved flees. Tanjiro goes for the demon’s neck, his weakspot, but the demon thinks his neck is too strong to break as Sabito broke his sword trying to cut it. Tanjiro’s strike however, severs the head.