"What is so interesting about taking lives? What do you find fun in killing?" the first and the last voice that made the demon tremble to his bones.
Yoriichi Tsugikuni was one of the twin children of the Tsugikuni clan. He was born somewhere in the middle of the Sengoku period. At that time, twins were considered an ill omen, signifying evil and damnation. Since his birth, Yoriichi had a scar-like birthmark on his forehead that prompted his father to kill him but was stopped by their benevolent mother, Akeno, who fell into rage having her husband say that. They collectively agreed that he would be sent off to a temple to become a monk when he would be ten years old.
On the other hand, his twin brother received warm affection from his parents. Michikatsu often visited his brother in his room, where he was given scarce food and frail shelter. His room was a small space made of three tatamis at the farthest end away from the rest of the house.
The chosen one from birth
Yoriichi's mark on his forehead bore him incredible prowess and might, more fantastic abilities to see people transparently. Despite being a symbol of a bad omen, his forehead served a good purpose for his growth. His mother, Akeno, made the hanafuda earrings as a symbol of divine blessings showered on him. Yoriichi was always a quiet child, which prompted others to think he was deaf. Despite the shortcomings of his poor childhood and the differentiated treatment he got from his family, he grew up to be the symbol of terror among the demons, given that the Demon Lord trembled whenever he heard his name.
Growing up in a house where his brother was treated with significant favoritism, he was neglected. Once when he was seven, seeing his brother Michikatsu practice for becoming a samurai, he voiced his wish to be the same. One of the men who was tasked to train his brother mocked him with one of a simp[le stance, but Yoriichi, after seeing it just for once, mastered it and landed more blows on the man than Michikatsu could ever do. These were the starting signs of one of the preliminary breathing styles.
Om their mother's demise from an illness, Yoriichi went to Michikatsu's room to bid him farewell as he was leaving for the temple and tucked the flue that Michikatsu gifted him, saying he would treasure it and his memories. Later, the pages of their mother's diary revealed to Michikatsu that Yoriichi was aware of their mother's illness and was said to be the heir. Michikatsu would be sent to the temple instead, but he ran away to spare his brother the pain. Despite this act of unconditional kindness and love from Yoriichi, it made Michikatsu extremely hostile toward him. He became envious of his brother and would try his best to surpass him in every way, gaining more hatred towards him.
The way to become the undefeatable
The story that paved Yoriichi's way to becoming a demon slayer is exceptionally tragic. When he ran away from his family, he ran for one day and one night but did not stop or show any exhaustion. He ran into the mountains, where he met a girl named Uta, with whom he lived for ten years before deciding to marry. They got married into a simple domestic life, even with Uta expecting their child.
When Yoriichi left to find a midwife for the delivery, he lost track of time helping a man find his way, so he decided he would depart for his home and look for a midwife the next day. When he returned home, he beheld the horrific sight of seeing his wife and unborn child's carcass lying in their hut because a demon had killed them. Unable to recover from the shock, he held on to them for ten days until he finally buried them, as another demon slayer insisted that he let go. This became the foundation day of Yoriichi's life as a demon slayer. His mark on the forehead bore immense talent and prowess for him to become the strongest demon slayer.
Reunion of the lost twins
His reunion with his brother happened when demons entirely extinguished Michikatsu's samurai encampment, and he was the only survivor. Yoriichi, with his impeccable swordsmanship, killed the demon that caused so much massacre and apologized for the demise of the other samurais. He named his breathing technique the Sun Breathing, which he mastered. This technique helped him be impeccable at swordsmanship and kill demons effortlessly.
He tried to impart this breathing style to other demon slayers, but it was a callous form to perfect, which left him to create diversified versions of this technique to match the capabilities of the demon slayers. Thus came the variation of the Sun Breathing as the Water, Wind, Flame, Stone, and Thunder styles of breathing. Michikatsu, being unable to master this breathing, created his style of breathing, Moon Breathing.
The final rendezvous with the Demon God
As quests after quests bring him success, thanks to his incredible prowess and the maestro at unreachable skills, he finally meets Muzan, the progenitor and the head of the demons. Tamayo accompanied him on their mission to kill and slaughter people. Yoriichi, who could see a person with transparency and read their mind, immediately got aware of the malicious and inhumane intent of Muzan. His tremendous desire to kill people and bring them massacre made Yoriichi fume with daunting rage.
Yoriichi's purpose to be born struck him, that he was born to defeat this enemy of humankind once and for all. In his duel with Muzan, he destroys parts of him with his capabilities. He discovered that Muzan has seven hearts and five brains that change their location to stay away from enemies' strikes. Yoriichi, at Muzan's bloodthirst and formidability, felt fear and went on to defeat him. He destroyed parts of him that we're unable to regenerate, yet at the climax of the fight, he could not defeat him because Muzan split into different pieces, of which, Yoriichi could only defeat 1500 of the 1800 pieces.
Meeting his defeat, he soon turns to Tamayo, who, to his surprise, sees her in relief to see Muzan's dismembered pieces. He comes to know about Tamayo's real nature and lets her go. Unable to defeat the greatest demon, letting a demon go, and returning to the news that his brother betrayed the demon slayer corps and became an Upper Moon Demon under Muzan, Yoriichi was banished from the demon slayer corps. With nothing left to lose, he sets out to his friends' house to stay for a while and independently defeat demons. His friends Sumiyoshi and Suyako were the Kamado family, to whom he left his earrings when he last visited them. In this way, the hanafuda earrings got passed down to the lineage of the Kamado family.
The last brotherly meeting
Independently defeating demons with his ever-impeccable fighting style and spirit, he finally faces off with his brother, who changed from Michikatsu to Kokushibo, the strongest Demon under Muzan. At that time, the ones who bore the mark of Demon slayers had only a lifespan of 25 years, but Yoriichi reached his 80s with his strength and might. Kokushibo, a demon, was immortal and was still envious of seeing Yoriichi live up to such an age.
Seeing his aged countenance and body disgusted Kokushibo, it soon turns into terror when he sees that Yoriichi still harbors the same courageous fighting spirit and swordsmanship. Kokushibo would have been defeated if not for the untimely and tragic death of Yoriichi in the middle of their duel. Still, it also holds testimony that Yoriichi is the undefeatable, strongest demon slayer ever. Kokushibo strikes his corpse, only to find the flute he once gifted Yoriichi when they were young. The last fight ends with the undefeatable one breathing his last, defeated by time only and no one else.