Mount Kumotori

Mount Kumotori is a mountain along the border of Tokyo, Saitama, and Yamanashi Prefectures. It is covered in thick snow.

Synopsis
After Yoriichi Tsugikuni ran away from his home, he ran straight for one day and one night without any sign of exhaustion, He ended up in Mount Kumotori, where he met a girl around the same age as him named Uta, whose entire family had died. Yoriichi chose to live with her in her house at Mount Kumotori and after 10 years, Uta and Yoriichi had married: the former becoming pregnant later. Just before the expected arrival, Yoriichi left home to summon a midwife, promising his wife to be back before the sun set. On his way, Yoriichi had helped an old man and lost so much time that he decided to return home and summon a midwife the next day. By then the sun had already set: when he finally arrived home he found that Uta and the unborn child were killed by a demon. The tragedy shocked Yoriichi so much that he held her corpse in his arms for ten days straight and only buried them after a pursuing Demon Slayer encouraged him to do so. This led Yoriichi to pick up his blade again and train as a Demon Slayer, leaving the house at Mount Kumotori abandoned.

When charcoal makers Sumiyoshi and Suyako are newlyweds, they find an abandoned house at Mount Kumotori to move into. It was the same house that had been lived in before, by Yoriichi and Uta. After moving in, Suyako gave birth to a son and a daughter. Their family are also later attacked by a demon, and rescued by Yoriichi, who happened to be swinging back through the area. Yoriichi then became friends with this family.

After Yoriichi's encounter with Muzan Kibutsuji, he was banished from the Demon Slayer Corps. Yoriichi decided he had much on his mind and wanted someone to talk to. He could only picture his friends Sumiyoshi and Suyako and decided to visit them. He goes back to the house at Mount Kumotori, sat down with Sumiyoshi, and told him his entire story, from his beginning to his banishment from the Demon Slayers. Reminded of his tragedies and speaking of his regret at letting Muzan live and the countless death that would follow, Yoriichi grew despondent. Sumire arrives at that moment to ask for a hug. At Sumiyoshi's request, he lifts her up, making her laugh and squeal with joy, causing him to break down in tears and embrace her. Suyako arrives shortly after to comfort him and treat Yoriichi to a meal and cheer him up.

While with the Kamados, Yoriichi would be asked by Suyako to perform the Sun Breathing's forms. He kindly did so, performing all the moves with such grace, he was likened more as a spirit that a human. Sumiyoshi would watch these demonstration intently and keep them in his memories. On this last visit at Mount Kumotori, despite being told he was welcome at any time, Yoriichi gave Sumiyoshi his Hanafuda earrings. Sumiyoshi and Suyako realized then this was going to be the last time he would visit. Overcome with emotion, Sumiyoshi called out to Yoriichi as he walked away, telling him to stop saying that he was a man of no worth. He reminded him that he saved them and promised to preserve the Sun Breathing's forms through his descendants. Hearing this, Yoriichi turns and smiles brightly, thanking the Kamados and waving them farewell. Through Sumiyoshi and Suyako, Sun Breathing would later be passed down to future generations with great detail as Hinokami Kagura, a way to keep it hidden and safe.

Many generations later, Tanjiro Kamado is living in the same house at Mount Kumotori with his parents and siblings. He goes to the town to sell some charcoal. 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 and Tanjiro takes refuge in Saburo's house for the night in case of a demon attack. Once the sun rises, Tanjiro makes his way back and discovered the house to be completely ransacked and all his family presumably dead. As his younger sister 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 the mountain, 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. Giyu Tomioka appears and tries to attack Nezuko, but Tanjiro begs him and insists that she wouldn't harm humans. After realizing that Nezuko attempts to kill him to protect Tanjiro, while wounded and fighting against eating her brother for food, he opts to spare her and knocked them both unconscious. Tanjiro wakes up to see Nezuko with a bamboo muzzle and is instructed to find Sakonji Urokodaki. After burying his family in the front yard of their house, Tanjiro takes Nezuko’s hand and together and they leave their home at Mount Kumotori.