Chapter 1

Cruelty is the first chapter of Koyoharu Gotōge's Kimetsu no Yaiba.

Summary
A young boy is seen carrying his unconscious sister on his back through a snowy path. She is bleeding and the boy tells her to stay alive, as he will try to save her. This boy is Kamado Tanjirou and his sister, Kamado Nezuko.

He remembers the events that happened a day before.

Tanjirou's lives on the mountain. As the New Year was near, he intended to go into town to sell some charcoal even though it would snow soon. After saying good bye to his mother and his siblings, Nezuko, Takeo, Hanako, Shigeru, and Rokuta, he left for town.

Everyone in town was happy to see Tanjirou. One of the villagers asked Tanjirou to take a whiff of a broken vase to see who the culprit was, to which Tanjirou pointed out that it was a cat's doing.

As he started to walk home in the evening, Mr Saburou forbade him from going back to the mountains as the sky was about to turn dark. Tanjirou told him not to worry as his nose can smell anything but Mr Saburou told him to take refuge in his house for the night in case of a Demon attack. Tanjirou then gave in to the persistent man. Although he dismissed Mr Saburou's words, Tanjirou remembered that his grandmother said the same thing before she passed away.

Once the sun rose, Tanjirou made his way back. The first thing he saw was a bloodied Nezuko and Rokuta lying on the snowy ground. Terrified, he went to check the house. It looked ransacked, and there were blood splatters everywhere. Everyone in his family is dead. His mother died protecting Hanako, and Takeo and Shigeru were lying beside them. As Nezuko was the only one with some body warmth, Tanjirou hurriedly brought her to see a doctor.

On the way down, Nezuko started to come to life. She tries to bite him with her fangs but Tanjirou was able to block the attack with his axe handle. Many questions emerged in Tanjirou's mind in a split second– was Nezuko a demon? But isn't she a human? Was she the one that killed his family? He theorizes that she did not kill them as she had a different scent from the person who attacked his family.

As she was pinning him down, her body and strength grew. Tanjirou suddenly felt guilt and remorse for not being there for his family, and even more so for his sister, as he was not able to save her from becoming a Demon. He felt that her new Demon blood would overpower her, therefore he decided to try to save her from taking her first victim– her own brother.

He tried to appeal to her humanity, or what's left of it. Tanjirou encouraged her to stop, and to try her best to hold the Demon blood back. Eventually, she stopped and started to cry; and upon seeing her tears, he cried too.

Suddenly, a man tried to strike at Nezuko. Tanjirou rolled himself and Nezuko away to avoid the attack. This katana wielding man asked why Tanjirou was protecting a Demon. Tanjirou told him that Nezuko is his sister, but the man still insisted on killing her. Tanjirou begged him and reasoned that Nezuko has not killed anyone, he will stop her from killing anyone, and that he will find a cure for her. Angrily, the swordsman went on a tirade telling Tanjirou that he was too weak to protect himself, let alone his sister. However, deep down, the swordsman felt slightly guilty as he arrived too late to prevent Tanjirou's family from being killed.

While Tanjirou was left forlorn, the swordsman stabbed Nezuko in the chest, causing her great pain. Tanjirou immediately threw a rock at him and charged at him. The man became angry, as it was merely an emotionally charged attack. He knocked Tanjirou out cold but realizes that Tanjirou was not carrying his axe. He looks up into the sky and nearly dodges a falling axe attack. The swordsman then becomes aware of Tanjirou's resolve to save his sister while sacrificing even his own life. Tanjirou had used the rock to distract the swordsman while he threw his only weapon in the air, leaving himself defenseless as Tanjirou put in motion the plan to take out both himself and the swordsman.

While the swordsman was distracted, Nezuko rushed to Tanjirou's motionless body. The swordsman cursed for letting his guard down, as he will now be witnessing a Demon attack. However, he was unprepared for what he was going to see. Nezuko was defending her brother from him! The swordsman then recalled that there was a person who once said the same thing– that the Demon would not eat anyone, but the person was eaten by that very Demon in the end. Demons high up in the mountains will even eat their parents and siblings if they're hungry. This Demon in front of him not only did not eat her brother to replenish her already starving condition, her defensive stance was also warning the swordsman not to hurt Tanjirou. She then charged at the swordsman who decided to sheath his sword.

Feeling that she will be different from the other Demons, he knocks her out too instead of killing her.

As he was unconscious, Tanjirou dreamt that his dead mother and siblings were surrounding him. His mother apologized for leaving him and told him that she will be leaving Nezuko in his care. Tanjirou woke up with tears in his eyes, and Nezuko, with a bamboo in her mouth to rein her fangs, still lying unconscious beside him. They were still alive.

The swordsman appears behind a tree and asked them to look for an elder named Urokodaki Sakonji and to tell him that Tomioka Giyuu sent them. He also advised Tanjirou not to bring his sister out in the sun before disappearing.

Tanjirou then buried the dead members of his family beside his house while Nezuko looked on dazedly.

Finally, the boy took Nezuko by the hand and they started on their journey to look for this man named Urokodaki Sakonji.

Characters in Order of Appearance

 * Kamado Nezuko
 * Kamado Tanjirou
 * Kamado Kie
 * Kamado Shigeru
 * Kamado Hanako
 * Kamado Takeo
 * Kamado Rokuta
 * Saburou
 * Kamado Tanjirou Sr.
 * Tomioka Giyuu

Events
Kamado Tanjirou's whole family is killed by a Demon, and his sister, Kamado Nezuko is turned into a Demon.