A young boy, Tanjiro Kamado, carries a visibly-wounded, unconscious girl through a snowy path on his back. This girl is revealed to be his younger sister, Nezuko Kamado. Tanjiro treks frantically through the snow and begs her to stay alive, vowing he would save her.
The scene cuts to a flashback of events that had occurred the day before. As the New Year arrives, Tanjiro intends to go to town and sell some charcoal in order to have enough food on the table for the holiday. His younger siblings, Hanako Kamado and Shigeru Kamado, overhear him and beg to go as well, but their mother sternly refuses, saying they would only cause him trouble. Tanjiro calls out to his younger brother, Takeo Kamado, and asks him to chop the firewood while he's away, much to the latter's disappointment as he hints that he wanted to chop wood with his older brother.
Tanjiro bids farewell to his mother and siblings as they remind him to stay safe. As he sets off, he runs into Nezuko who is rocking the youngest child, Rokuta Kamado, to sleep. She mentions their younger siblings' attachment to Tanjiro, and they depart.
As Tanjiro arrives in the town, everyone is delighted to see him and immediately call him over to buy some of his charcoal. One of the villagers cries out to Tanjiro and asks him to take a whiff of a broken vase to figure out who the culprit was. The boy's keen sense of smell is able to detect that it was a cat at fault and not the villager who was being held responsible for it.
As the sun begins to set, Tanjiro begins his journey home. However, as he begins to ascend the mountain, he is stopped by an elder by the name of Saburo. The man forbids him from going back to the mountains as the sky was turning dark. Tanjiro tells him not to worry as his nose can quickly smell out danger, but Saburo insists he take refuge in his house for the night in case of a Demon attack; Tanjiro finally gives in to the persistent man. Although he dismisses Saburo's words, he remembers that his grandmother said something similar about Demons before she passed away.
Once the sun rises, Tanjiro makes his way back but suddenly smells blood when he nears his home. The first thing he sees is a bloodied Nezuko holding Rokuta lying on the snowy ground. Terrified, he goes to check the house and is shocked to see the ransacked building and bloody mess, everyone in his family presumably dead. As Nezuko is the only one with warmth in her body, Tanjiro hurriedly carries her on his back to see a doctor.
On the way down, Nezuko starts to come to life. She tries to bite her brother with her fangs, but Tanjiro is able to block the attack with his axe handle. Many questions emerge in Tanjiro's mind as he wonders if Nezuko was a Demon and killed their family, despite being born human. He deduces that she did not kill them as she had a different scent from the individual who attacked his family.
As his sister pins him down and her body and strength grow, Tanjiro suddenly feels guilt and remorse for not being there for his family, and even more so for his sister, unable to save her from becoming a Demon. He feels that the new Demon blood would overpower Nezuko and tries to prevent her from taking him as her first victim.
Tanjiro starts attempting to appeal to what is left of his sister's humanity, encouraging her to stop and do her best to hold the Demon blood back. Eventually, she ceases her struggle and starts to cry; upon seeing his sister's tears, Tanjiro cries as well.
Suddenly, a man strikes at Nezuko. Tanjiro rolls himself and Nezuko away to avoid the attack. The katana-wielding man asks why Tanjiro was protecting a Demon. Although Tanjiro tells him that Nezuko is his sister, the man insists on killing her. Tanjiro begs and reasons that Nezuko has not killed and will not kill anyone, and he will find a cure for her. Angrily, the swordsman goes on a tirade, telling Tanjiro that he was too weak to protect himself, let alone his sister. However, deep down, the swordsman feels slightly guilty as he arrived too late to prevent Tanjiro's family from being killed.
While Tanjiro is left forlorn, the swordsman stabs Nezuko in the chest, causing her great pain. Tanjiro immediately throws a rock at him and charges. The man becomes angry over what was merely an emotionally-charged attack. He knocks Tanjiro out cold but notices that he was not carrying his axe. He looks up into the sky and nearly dodges a falling axe attack. Through this carefully-planned assault by the young boy, the swordsman becomes aware of Tanjiro's resolve to protect his sister, sacrificing even his own life in order to save her from him.
While the swordsman is distracted, Nezuko rushes to Tanjiro's motionless body. The swordsman curses for letting his guard down, expecting Nezuko to devour her brother. However, Nezuko instead defends her unconscious brother, using her own body to shield him. The swordsman recalls there was a person who once said their Demon-turned relative would not eat anyone, but in the end, the person was eaten by that very Demon. Demons high up in the mountains would even eat their parents and siblings if they were hungry, but the Demon in front of him did not eat her brother and even defended him, despite her already-starving condition. She charges at the swordsman and he sheathes his sword. Feeling that she was different from other Demons, he knocks her out instead of killing her.
As he is unconscious, Tanjiro dreams that his dead mother and siblings were surrounding him. His mother apologizes for leaving him and tells him that she will be entrusting Nezuko to his care. Tanjiro wakes up with tears in his eyes, and Nezuko, with a bamboo muzzle in her mouth to rein her fangs, laid unconscious but alive beside him.
The swordsman appears behind a tree and asks them to look for an elder named Sakonji Urokodaki, who lives at the foot of Sagiri Mountain, and to tell him that Giyu Tomioka sent them. Before disappearing, he advises Tanjiro to not bring his sister out in the sun.
After Giyu's departure, Tanjiro buries the dead members of his family beside their house while Nezuko looks on. The Kamado siblings take each others' hands and starts on their journey to look for Sakonji.
Characters in Order of Appearance
- Nezuko Kamado
- Tanjiro Kamado
- Kie Kamado
- Shigeru Kamado
- Hanako Kamado
- Takeo Kamado
- Rokuta Kamado
- Tanjuro Kamado
- Giyu Tomioka
- Tanjiro Kamado's whole family is killed by a Demon.
- Nezuko Kamado is turned into a Demon.
- Tanjiro Kamado and Nezuko Kamado vs Giyu Tomioka