Yoriichi Tsugikuni

Yoriichi Tsugikuni was a member of the Demon Slaying Corps during the Sengoku Era. He was the younger twin brother of Michikatsu Tsugikuni, who became a demon, Kokushibo.

Appearance
Yoriichi looks identical to the human form of Kokushibo. He has the same facial features, hairstyle and hair color, and even his Demon Slayer Mark is at the same place as the top of his forehead. However, Yoriichi is slightly more slender and wears a red over a white kimono with a black hakama on his waist. He also has the same hanafuda earrings that Tanjiro Kamado and Tanjuro Kamado have, and carries a katana on his hip as the custom for the Demon Slayers.

In his old age he gained white hair and was blinded by unknown means.

Personality
Yoriichi was a calm and respectful individual. He was extremely humble, seeing himself as just any other man and no one special. Yoriichi was also noted by his brother to always have had faith in the future and was confident that despite the already overwhelming power the Demon Slayers of the first Breath possessed, a generation would emerge that will further surpass their own. As a child, it was shown that Yoriichi adored and idolized his older brother Michikatsu, even declaring that he will support his brother's dream of becoming the strongest Samurai in the land, and that he would become the second strongest; in his childhood, he was also extremely reserved and quiet, even being thought deaf by his family for seven years as he never spoke.

When he met his older brother again after sixty years, the latter having embraced his new life as a demon, he was deeply devastated and pitied his brother for what he had became, attempting to kill Michikatsu himself in order to stop him,later it was shown that despite his brother becoming a demon and abandoning and betraying the Demon Slayer Corps,Yoriichi still treasured the handmade flute made by Michikatsu showing that he still loved and treasured his memories with him.

History
Yoriichi and his twin brother Michikatsu were born into the Tsugikuni clan in the Sengoku period, a time when twins were considered to be an extremely bad omen. Yoriichi in particular was born with an odd birthmark on his forehead, which caused his father to declare that he would kill him; however, their mother flew into a rage, and it was eventually agreed upon that Yoriichi would be sent to the temple to become a monk when he turned ten years old. Despite their father's belief that the mark was unlucky, it actually granted Yoriichi incredible physical prowess and the ability to see the bodies of living things in transparency. Yoriichi grew up very differently from Michikatsu, being given much poorer food and education than his brother and being confined to a small three-tatami room away from the rest of the house. Until he was seven, Yoriichi was thought deaf, as he never spoke, and was constantly found clinging to his sickly mother's left side (it is later revealed that he sensed her illness weakening her left side, and was helping to support her while she walked); because of this, Michikatsu found him pitiful. Still, his brother often snuck behind their father's back to see Yoriichi, even giving him a handmade flute as a gift to comfort him.

One day at age seven, as Yoriichi watched Michikatsu practicing sword swings, he smiled and spoke for the first time, declaring his intent to become a samurai like his brother, startling Michikatsu. However, Michikatsu was dismissive of this sentiment, as it was well-known that Yoriichi would be sent to the temple when he was ten. Still, one of their father's men tasked with training Michikatsu decided to humor Yoriichi, showing him a simple stance. Unexpectedly, Yoriichi flew into action after assuming this stance, landing four blows against the man and shocking his brother, who, despite his training, had never even landed one. However, Yoriichi couldn't stand the feeling of hitting someone and renounced his goal to become a samurai. Michikatsu often asked him about how he managed to hit the man and Yoriichi described what was likely an early form of Breath Style, but rather than talking about the sword and continue training in the sword, he happily told Michiktasu he would rather play sugoroku and fly kites with him instead.

Yoriichi and Michikatsu were seven when their mother finally passed away from her illness, prompting Yoriichi to come to Michikatsu's room at night to tell his brother the news and bid goodbye, as he planned to leave for the temple that night. He expressed gratitude for his brother, stated that he would always keep him in mind, and fondly tucked away the flute Michikatsu had made for him earlier. It was later revealed to Michikatsu through their mother's diary that Yoriichi had known everything about their mother's illness, and had prepared to leave the night she died in order to protect his brother from being stripped of his title as successor and sent to the temple in Yoriichi's place. However, this caused Michikatsu to develop an intense hatred of Yoriichi, who he believed to be a genius and was extremely envious of.

Eventually, Yoriichi and Michikatsu went on to become incredibly strong Demon Slayers, developing their own Breath Styles, Yoriichi's being the Breath of the Sun. Yuriichi went on to teach many people of the breathing techniques he used and of the Breath of the Sun, however since no one could reach his strength different derivatives began to emerge from the Breath of the Sun including the Breath of The Moon used by Michikatsu. Once the two gained their Demon Slayer Marks, Yoriichi expressed his plan to have a successor, despite his brother believing none could rise to their potential. Eventually the two would part ways and Yoriichi would continue becoming stronger and hunting demons for sixty years. Despite the death sentence of 25 years of life imposed by the Demon Slayer Mark, Yoriichi somehow survived to his elderly years, but somehow lost his sight during this time period.

Synopsis
Based on the past memory Tanjiro had from his ancestor, Sumiyoshi and Yoriichi had some sort of relationship, if not a friendship, given that Yoriichi would frequently stop at Sumiyoshi's house for food and tea. It is also implied by Sumiyoshi that Yoriichi saved his life at some point before the birth of his child. Based on the conversation we come to know that Yoriichi had no successor both as a swordsman and in a familial sense. He also seemed mournful, likely of the fact that his brother turned into a Demon, loyal to Muzan.

Abilities and Powers
He is arguably the strongest Demon Slayer and swordsman in the entire history of the series, given that he was the one who cornered Muzan Kibutsuji and had him on the verge of death until he managed to escape. Shortly before his death and at least 85 years in age, he battled his older twin brother, Kokushibo (UM1). Despite his extreme age and apparent blindness, he quickly gained the upper-hand in the battle with a single move, even slitting his throat before he finally died standing up, unscathed. Kokushibo himself admits that if Yoriichi launched a second swing before dying, he would have killed him.

Natural Abilities

 * Demon Slayer Mark: A special marking that appears on strong Demon Slayers. Its specific abilities are unknown, but what is know is that it drastically improves the abilities of the Demon Slayer, making them much stronger, faster and able to react quicker then they can achieve normally, though at the cost of being cursed to die at the age of 25. Unlike all other marks users in his era, Yoriichi was able to defy fate and lived to 85 years of age. It is presently unclear why Yoriichi is immune to the Mark's effects. Unlike all other mark users, he is born with this ability naturally.


 * See-Through World (きる Sukitōru Sekai?) - Yoriichi has the ability to see the "see through world", allowing him to see the muscles, blood flow, and joint movement of his opponents. He can accurately predict and anticipate the movements and attacks of his opponents with this ability. Unlike all others users, he is born with this ability naturally.

Swordsmanship
Breath of the Sun (の) None of the techniques of the Breath of the Sun have been directly shown. However, Yoriichi in his old age is shown to have used it in his battle against Kokushibo 400 years prior to the present time of the story.

Quotes

 * In Chapter 174 prior to dueling his brother with the intent of killing him, he states: "My sympathies, my brother."

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