Yoriichi Tsugikuni

Yoriichi Tsugikuni was a member of the Demon Slayer Corps during the Sengoku Era. He was the younger twin brother of Michikatsu Tsugikuni, who later became Upper Moon One, Kokushibo.

Appearance
Yoriichi looked identical to Kokushibo when he was Michikatsu Tsugikuni, although there were notable differences. He was slightly more slender and had shorter bangs and wavier hair than his brother, colored black with red tips (burgundy in the anime, similar to Tanjiro Kamado). His Demon Slayer Mark was at the same place at the top of his forehead as Tanjiro, albeit lighter in color.

Yoriichi wore a red haori over an orange kimono with black hakama and a katana carried at the waist, conventional to most Demon Slayers. He sported the same hanafuda earrings passed down to Tanjiro Kamado from Tanjuro Kamado.

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 would further surpass their own. Normally, Yoriichi shows little to no emotion. However, Yoriichi does express emotions such as sadness, when he met his brother again during the final moment of his life, or when the baby Sumire want to hug him.

As a child, it was shown that Yoriichi adored and idolized his older brother, Michikatsu, even declaring that he would support his brother's dream of becoming the strongest Samurai in the land, and Yoriichi himself 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, Yoriichi was deeply devastated and pitied his brother for what he had became. He attempted to kill Michikatsu himself in order to stop him as a traitor of the Demon Slayer Corps. However, despite his brother's betrayal, Yoriichi still treasured the handmade flute he gave to him, showing that he still loved and enjoyed 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 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, Yoriichi smiled and spoke for the first time, declaring his intent to become a samurai like his brother after watching Michikatsu practice sword swings, 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, the young boy flew into action after assuming the 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 a Breath Style, but rather than talking about the sword and continue training in the sword, he happily told Michikatsu he would rather play sugoroku and fly kites with him instead.

When their mother passed away from her illness, Yoriichi went to Michikatsu's room at night to tell his brother the news and bid farewell, planning to leave for the temple that night. He expressed gratitude towards his brother, stating 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 him.

Even though he was to become a monk at a temple, did Yoriichi not do so, instead running away, wanting to live freely. After running straight for one day and one night without any sign of exhaustion into the mountains, Yoriichi met a girl around the same age as him named Uta, whose entire family had died. Yoriichi choose to live with her and after 10 years, Uta and Yoriichi became married and Uta became pregnant with his child. But just before the expected arrival of their child, Yoriichi left home to summon a midwife, promising his wife to come back before the sun sets. On his way Yoriichi had helped an old man, loosing so much time that he decided to return home and summon a midwife the next day. Upon then the sun then had already set and when he finally arrived home did he found Uta and their unborn son laying on the ground, both killed by a Demon. The tragedy shocked Yoriichi so much that he held their corpses in his arms for straight ten days and only buried them, after a pursuing Demon Slayer encouraged him to do so. This was the cause for Yoriichi to pick his blade back up and train as a Demon Slayer.

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, Michikatsu's being the Breath of the Moon. Yoriichi 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, Yoriichi instead trained his apprentices individual altered breath style training to better suit their individual strengths and weakness,eventually causing different derivatives to emerge from the Breath of the Sun. 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.

At some point Yoriichi encountered Muzan Kibutsuji the progenitor demon and mortal enemy of the Demon Slayers accompanied by Tamayo. Upon meeting him Yoriichi could feel his rampant malice and violent intent that he believed was like boiling magma from a volcano ready to consume everything, it was then he reasoned he was born with natural talent to defeat Muzan once and for all. Muzan stated to Yoriichi that he had lost interest in swordsmen who employ breathing techniques as had encountered and slaughtered many of them. As soon as he said that, Muzan performed long sweeps trying to kill Yoriichi who instantly realized any of those attacks would be fatal and felt fear for the first time. Thinking he was born to kill this demon, Yoriichi fought Muzan and was able to discern Muzan's assemblage of seven hearts and five brains spread on his body, and was successfully able to cut through all of them with his Thirteenth Form.

Muzan was left in disbelief as he was unable to regenerate while struggling to keep his head attached. Yoriichi noticed Tamayo was hopeful for Muzan's destruction and the swordsman asked Muzan what was the value of life to him. Muzan didn't respond but instead grinded his teeth with his skin turning red from anger, and suddenly he bursted into 1,800 lumps of flesh of which Yoriichi cut 1,500 in mere seconds. He correctly deduced the remaining lumps must have reformed to regenerate somewhere else.

Tamayo was left on the verge of tears as she realized Muzan learned how to avoid death by decapitation and how the man that ruined her life remained alive. Yoriichi calmed Tamayo who proceeded to tell him that Muzan would likely avoid facing Yoriichi again and how she was glad to have been freed of Muzan's control due to being weakened. Yoriichi requested for Tamayo's help to which she reluctantly agreed. Soon after some demon slayers report to Yoriichi that his brother, has betrayed the organization becoming now the demon Kokushibo. This along with Yoriichi's failure in killing Muzan infuriated many who wanted him to step down. The new head of the demon slayers, however, disagreed with this, although Yoriichi felt guilty for placing a huge burden on a six years old boy.

Despite the apparently limited lifespan of 25 years suffered by those who bore the Demon Slayer Mark, Yoriichi somehow live for many more decades, but eventually went blind as he continued slaying demons. Later on his 80s, he would personally confront his brother, now Muzan's strongest lieutenant as Upper Moon One. Devastated at what his brother had become and trying to free him from his current fate, Yoriichi tried killing his brother, but only slightly sliced Kokushibo's neck. Although Kokushibo feared the next blow would kill him, Yoriichi unfortunately passed away soon after. Kokushibo would strike at his brother's corpse in scorn, only to realize Yoriichi carried the flute the former gifted him as children. Remorseful and mourning the brother he always envied, Kokushibo would take the split flute and carried it with him at all times until his eventual death.

During the present battle against Muzan, Tanjiro in the verge of death through Muzan's blood would eventually see Yoriichi's past memories and even though he died hundreds of years ago, wish that his spirit could find peace.

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 hinted by Sumiyoshi that Yoriichi saved his life at some point before the birth of his child. From this, it could be implied Yoriichi had no successor both as a swordsman and in a familial sense. He also seemed mournful, likely because of the fact that he was unable to save his family, defeat Muzan, or prevent his brother from turning into a Demon.

Abilities and Powers
Yoriichi 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 of at least 85 years in age, he battled his older twin brother, Kokushibo. 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 it drastically improves the abilities of the Demon Slayer, making them much stronger and faster with a quicker reaction than can be achieved 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 about 85 years of age. It is presently unknown why Yoriichi is immune to the Mark's effects. Unlike all other mark bearers, he was born with this ability naturally.


 * See-Through World (きる) - Yoriichi had the ability to see the "see through world", allowing him to see the muscles, blood flow, and joint movement of his opponents. He could accurately predict and anticipate the movements and attacks of his opponents with this ability. Unlike all others users, he was born with this ability naturally.
 * Master Swordsman: Yoriichi was an extremely powerful and skilled swordsman. Even as child with no training, he was capable of easily defeating a trained swordsman the very first time he ever picked up a sword.
 * Immense Speed: Yoriichi possessed immense levels of speed, with which he was able to move fast enough to slit Kokushibo's throat without the latter being able to counter him, despite him being on guard and Yoriichi's blade was slightly near his throat. Sometime before, during his battle against Muzan, he also managed to near-fatally injure Muzan with one move, despite the Demon's own inhuman speed and strength, and, when Muzan divided himself into 1,800 flesh pieces to escape, Yoriichi still managed to reduce the number down to a mere 500 in only seconds.
 * Crimson Red Nichirin Blade:  When fighting, Yoriichi had the ability to dye his normally black sword to crimson red, giving it the ability to hamper the enhanced regeneration of Demons, even Muzan's instant regeneration.

Swordsmanship
Breath of the Sun (の) So far only the thirteen form was shown. However, Yoriichi, in his old age, is shown to have used the breath style in his battle against Kokushibo 400 years prior to the present time of the story.

Trivia

 * The bag in which Yoriichi carried his brother's flute seemed to have been made of the cloth from Uta, his late wife's kimono, due to the similar patterns.

Quotes

 * (To Kokushibo) "My sympathies, my brother."