Mount Kumotori

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

History
After his mother died from illness when he was ten years old, Yoriichi Tsugikuni fled from his home. He ran straight for one day and one night without any sign of exhaustion. Eventually, he arrived at a place full of compact fields and paddies on Mount Kumotori. There, he met Uta, a girl of similar age who had tragically lost her entire family to a a widespread illness. Yoriichi made the decision to reside with Uta in her humble mountain hut, and over the course of ten years, their bond deepened, culminating in their marriage. During Uta's final month of pregnancy, Yoriichi left their home in order to summon a midwife to ensure a safe delivery for the child, hopeful to return before the sun set. On his way, Yoriichi encountered a feeble old man struggling to traverse the mountain. The man's son had been gravely wounded in battle, and Yoriichi chose to accompany the man see his son's final moments. He decided to fetch the midwife the next day. By then the sun had already set and when he finally arrived home as fast as he could, he found that Uta and the unborn child were killed by a demon. The tragedy shocked Yoriichi so much that he absentmindedly embraced her corpse for ten days straight and only buried them after a pursuing Demon Slayer, a Rengoku ancestor, encouraged him to do so. Yoriichi's dream for a peaceful life with his wife and child were tragically shattered by the existence of demons in the world. Driven by sorrow and a resolute purpose, Yoriichi decided to embark on a new path as a Demon Slayer, leaving behind his Mount Kumotori home.

Years later, newlyweds Sumiyoshi Kamado and Suyako Kamado stumble upon an abandoned hut on Mount Kumotori. Unbeknownst to them, this humble abode was once inhabited by Yoriichi and Uta. After Yoriichi's fateful encounter with Muzan Kibutsuji and subsequent exile from the Demon Slayer Corps, he returned to the house he once shared with his late wife. There, he ran into Sumiyoshi and Suyako, who was on the last month of her pregnancy, as they were being attacked by a demon. Without hesitation, Yoriichi rescued them from the demon. Afterwards, Suyako started going into labor and Yoriichi left to summon a midwife with unprecedented speed. The next day, Suyako successfully gave birth to a baby girl named Sumire Kamado. In the act of aiding this young couple, Yoriichi found a semblance of redemption, a bittersweet solace for his own unfulfilled longing for a family with his late wife.

While Suyako is asleep after labor, Sumiyoshi brings Yoriichi tea and some food. Yoriichi, who was cradling the peacefully sleeping Sumire in his arms, graciously accepts Sumiyoshi's hospitality. Apologetic for burdening a guest with the care of his child, Sumiyoshi expresses his gratitude to Yoriichi for saving their lives. Sumiyoshi apologizes to Yoriichi for having him to babysit his child as a guest. He offers to pass down the swordman's tale, acknowledging that even though his family is of humble origins as coal-burners, their lineage will carry on Yoriichi's legacy. However, Yoriichi humbly declines, assuring Sumiyoshi that destiny will find its way, and his heritage will be preserved. Reflecting on his own perceived shortcomings and inability to protect what mattered most, Yoriichi takes his leave.

Two years later, as Sumiyoshi is chopping wood in front of his house, he feels a tug on his robes and turns to see little Sumire pointing towards a man standing under a nearby tree, bowing respectfully. It is Yoriichi. They sit together on the porch, and Yoriichi explains that he has been burdened with many thoughts and needed someone to talk to. Seeing Sumiyoshi holding a grown Sumire, Yoriichi expresses his happiness in witnessing the joy of others and considers it a blessing to be born into this world. He proceeds to share his entire story, from his childhood to his exile from the Corps. Overwhelmed by the weight of his tragedies and his regret at failing to kill Muzan, knowing the countless deaths that would follow, Yoriichi becomes despondent. Sumiyoshi listens in silence, unable to find the right words to offer. It is during this moment that Sumire reaches for Yoriichi's haori. At Sumiyoshi's request, Yoriichi lifts her up, bringing forth her laughter and squeals of joy. Witnessing this heartwarming sight, Yoriichi breaks down in tears and embraces Sumire. Just then, Suyako returns from gathering chestnuts in the forest, with their son on her back. She sees Yoriichi hugging the child and comforts him, saying she will prepare a meal to uplift his spirits.

Later, Suyako persistently urged Yoriichi to demonstrate his Sun Breathing techniques. With utmost grace, he performed each move, appearing more like a celestial being than a mere mortal. Sumiyoshi observed every detail, etching the movements into his memory with unwavering focus. Suyako and Sumire were filled with elation, while Yoriichi humbly bowed his head, seemingly embarrassed by the attention. As Yoriichi prepared to depart, he presented Sumiyoshi with his Hanafuda earrings, a token of their time together. Despite the Kamado family's invitation for him to return anytime, they understood deep in their hearts that this was the last time they would see him. Overwhelmed by emotions, Sumiyoshi called out to Yoriichi as he walked away, urging him to cease speaking of himself as a man of no worth. Sumiyoshi reminded him of the profound impact he had made by saving their lives, vowing to preserve both the earrings and the forms of Sun Breathing through future generations of their lineage. Moved by these heartfelt words, Yoriichi turned back, his smile radiant, expressing his gratitude to the Kamados before bidding them a fond farewell.

Through the Kamado family, Sun Breathing would continue to be passed down with meticulous accuracy, taking the form of the hidden and sacred Hinokami Kagura dance, ensuring its preservation and protection. As the years passed, the Kamado family remained rooted in their ancestral home on Mount Kumotori, safeguarding the legacy of Yoriichi for countless generations to come.

Final Selection Arc
Tanjiro Kamado, a descendant of Sumiyoshi and Suyako, 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. Hashira 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.