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, Yoriichi did not do so, instead he ran 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 chose to live with her and after 10 years, Uta and Yoriichi became married and Uta became pregnant with his child. Just before the expected arrival of their child, Yoriichi left home to summon a midwife, promising his wife to come back before the sun set. On his way Yoriichi had helped an old man, losing so much time that he decided to return home and summon a midwife the next day. By then the sun then had already set and when he finally arrived home 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 ten days straight 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 Sun Breathing and Michikatsu's being the Moon Breathing. 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 the value of life was 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 had betrayed the organization and become 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 year old boy.

Despite the apparently limited lifespan of 25 years suffered by those who bore the Demon Slayer Mark, Yoriichi somehow lived for many more decades, but eventually went blind as he continued slaying demons. Later on in 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 to him when they were both still children. Remorseful and mourning the brother he always envied, Kokushibo took the split flute and carried it with him at all times until his eventual death.

During the present battle against Muzan, Tanjiro on the verge of death through Muzan's blood would eventually see Yoriichi's past memories and even though he died hundreds of years ago, wished 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.

Uta
Soon after he ran away from home Yoriichi encountered Uta in the mountains at a paddy, standing still all by herself holding a bucket in her hands. After a while, Yoriichi asked her what she was doing Uta replied that she was all alone now as her family had died due to a disease and felt lonely so she decided to take some tadpoles to her home but continued to stand still and as the sun began to set, she lowered her bucket and let the tadpoles go. Yoriichi asked her why she decided not to take them home with her and Uta responded that she felt bad about separating the tadpoles from their parents and siblings. Then the young boy offered to go with her instead and she agreed.

Uta was very talkative and contrasted well with Yoriichi's silent personality, she would talk all day and through her Yoriichi learned for the first time that the rest of the world saw things differently than him, discovering that being able to see through other living creatures was not something other people could do. As the pair lived together they grew quite close and whenever they went out Uta would always grab Yoriichi's hand very tightly, as if holding a kite whose string had been cut loose.

Ten years after they first met the two got married and in the final month of Uta's pregnancy, Yoriichi had to leave her at home as he went to fetch a midwife, however upon returning he found that his wife and unborn child had both been slaughtered in cold blood by a Demon. Yoriichi was deeply saddened by this and spent a full 10 days embracing their corpses until a Demon Slayer passed by and advised him to bury them. Uta meant a great deal to Yoriichi and he likely never married another woman after her as he had no heirs, in addition to also carrying a bag likely made from Uta's kimono with him for the rest of his life.

Kokushibo
Michikatsu Tsugikuni was Yoriichi's elder twin brother who was born only a few moments before him. Due to being older, he was in line to be their father's successor while Yoriichi was was to be sent off to a monastery when he was old enough. Yoriichi would be all alone by himself in their house while Michikatsu received all the attention as the heir to their father. Yoriichi would always cling to their mother and his brother found this to be pitiful. One day Michikatsu made his brother a wooden flute, a gesture the young Yoriichi appreciated greatly and even smiled for the first time ever upon receiving this gift. He would keep this flute with himself until the day he died. Wanting to spend more time with his brother Yoriichi attempted to learn sword fighting alongside him and greatly outclassed Michikatsu's teacher, who his elder brother had barely even managed to strike throughout his training. When their mother suddenly died of an illness Michikatsu found out that she had been weak in her left side due to the sickness and deduced that Yoriichi always clinging to their mother was in fact to support her and this greatly troubled Michikatsu, who quickly became jealous of his younger brother's prowess.

Their father had been planning on making Yoriichi his heir after learning of his exquisite swordfigthing skills but the young boy knew his brother had been trained his entire life to be the heir and suddenly having it snatched away from him would be devastating. So Yoriichi decided to run away from home to avoid that from happening.

Yoriichi looked up to his brother and bore him no ill will, even after years of separation he rushed to save Michikatsu when his forces were battling demons to protect their home. Swiftly dealing with them all, Yoriichi turned around and apologised to his brother for being late and not being able to save any of his men. Michikatsu was greatly jealous of his younger brother and upon seeing him again those feelings reignited and he followed him into the Demon Slayer Corps. He attempted to learn Yoriichi's Sun Breathing and while he was able to emulate it better than anyone else due to his close relationship and similarity to Yoriichi, he was still unable to perform it properly, creating a new form of Breathing called Moon Breathing.

Confident in his and his brother's progress, Michikatsu once declared to Yoriichi that they were the greatest swordsmen of all time and that no one else would ever be able to rival them. Yoriichi disagreed and told his brother that they were but small droplets in the vast history of the world and that there would surely come a time where someone who surpassed them would appear and that they should feel secure with this knowledge. Still frustrated at his continued failure to overtake Yoriichi, Michikatsu would continue to be jealous of his brother, so much so that when Muzan Kibutsuji approached him with the offer to turn him into a demon who could live forever he accepted, becoming Kokushibo, eventually Upper Moon One. When Yoriichi learned of this in the aftermath of his battle with Muzan he was greatly saddened and this was one of the factors that led to Yoriichi being exiled by the Demon Slayer Corps.

Many years later, wizened in his old age Yoriichi once again met his brother, preparing to battle him. Before he begins the battle he apologises to his brother with tears in his eyes and then steels himself to battle him. The brothers both attack each other but it is Yoriichi who gets the hit in, slicing his brother deeply through the neck leaving him but one blow away from death. However, Yoriichi lowers his blade and it sinks into the ground, with him leaning on it as he dies in battle. Frustrated at yet another failure to even land a blow on his brother Kokushibo slices through Yoriichi's dead body out of sheer anger. He sees that an object falls out of his brother's cloak and upon closer inspection sees that it is the flute he had made for him in their childhood. Kokushibo tears up at this touching gesture but is so far gone in his jealousy that he sees it as only more proof of his brother being superior to him.

Sumiyoshi
We are not told how Sumiyoshi and Yoriichi met, but based on the manga, we can see that Yoriichi and Sumiyoshi were good friends, though they did not see each other very often. After Yoriichi was banished from the Demon Hunters, he decided to visit Sumiyoshi, because he was the first person who came to mind when Yoriichi wanted to talk to someone about how difficult his life has become. He begins to explain the situation, as to where he let Muzan and Tamayo escape and how his brother became a demon and how he was banished from the Demon Slaying Corps, after which left Sumiyoshi speechless, with only tears streaming down his face. Then Sumiyoshi's daughter, Sumire, started to tug on Yoriichi's haori, to carry her. Seeing the joy on Sumire's face from being lifted up, made Yoriichi cry, when Suyako, Sumiyoshi's wife, returned from picking chestnuts. Later, Suyako asked Yoriichi to demonstrate all of the Breath of The Sun forms, to which Sumiyoshi engraved it into his mind. Just before Yoriichi left, he gave Sumiyoshi his Hanafuda earrings, when Sumiyoshi realised he would never see Yoriichi again and as Yoriichi left, Sumiyoshi promised to keep the earrings and told Yoriichi to never think he never accomplished anything and that he would carry on Yoriichi's legacy, to which Yoriichi replied "Thank You", before disappearing to never be seen again by Sumiyoshi.

Abilities and Powers
Yoriichi is arguably the strongest Demon Slayer and swordsman in the entire history of the series, being born with the Demon Slayer Mark and See-Through World. As a child untrained in swordsmanship, he was able to defeat a trained sword instructor and he was referred to as a miraculous prodigy. After training as a Demon Slayer, Yoriichi could defeat multiple demons to where his older brother stated that he as a child couldn't even compare to him as an adult. He alone among the Demon Slayer Corps was able to corner Muzan Kibutsuji and had him on the verge of death until he managed to escape. Yoriichi was considered to be a real monster by Muzan, both the progenitor and strongest among all Demons.

Shortly before his death of at least 85 years in age, he battled his older twin brother, Kokushibo who turned into a demon. Despite both his extreme age and apparent blindness, he quickly gained the upper-hand in the battle in 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 while commenting Yoriichi's power was still in his prime.

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. His swordsmanship was so tremendous that a battle doll was made to look like him and have 6 arms wielding katana utilizing 108 techniques only to imitate Yoriichi's skills.
 * 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 black sword to crimson red, letting him hamper the enhanced regeneration of Demons, even Muzan's instant regeneration, leaving permanent damage burned to his cells that haven't healed for hundreds of years.
 * Lack of Presence: During their first battle together, Muzan noticed that Yoriichi emanated absolutely no sense of drive, hatred or anger, fighting spirit, animosity or even bloodlust despite being in mid battle against him, rendering it practically impossible for Muzan to detect him or gauge how powerful he was upon first seeing him despite his immensely enhanced and practised Demon senses. This caused him to then severely underestimate Yoriichi, a judgement that nearly cost him his life, and the Demon Progenitor then deemed Yoriichi to be an even greater monster and more of a genuine Demon than he ever was.

Swordsmanship
Breath of the Sun (の): Created by Yoriichi himself as the original Breath Styles and so far has shown thirteen forms in total. Even in his old age, he has shown to be capable of using the Breath of the Sun against Kokushibo 400 years prior to the present time of the story.


 * Dance - A single high-powered slash seemingly releasing fire.


 * Raging Sun - The user unleashes two horizontal slashes to hit or intercept an enemy from the front or side.


 * Clear Blue Sky (の) - The user spins his body vertically to create a 360-degree slash.


 * Burning Bones, Summer Sun - A circular slash that defends from imminent frontal attacks.


 * Sunflower Thrust - A single thrust attack with the point of the blade.


 * Setting Sun Transformation - The user flips into the air to deliver an upended flaming sword slash.


 * Solar Heat Haze - The user charges towards the target, attacking it with a haze covered slash that seemingly fails to hit, but actually does hit.


 * Beneficent Radiance - The user spirals into the air to deliver a powerful slash to those caught in it.
 * Dragon Sun Halo Head Dance (の い Nichiun no Ryū Kaburimai?)  - Resembling a dragon, the user moves in circles to avoid enemy attacks and slashes then multiple times at the target.


 * Fire Wheel - The swordsman leaps behind the opponent and spins in the air while releasing a flaming attack in a circular motion.


 * Fake Rainbow - The user utilizes this technique to evade incoming attacks with high-speed twists and rotations, thus creating afterimages. The afterimages work most effectively on enemies with good vision as they will probably fail attack the afterimage instead of the actual body of the user.


 * Flame Dance - A two-combo strike which starts with a vertical slash and then a horizontal one right after.


 * Thirteenth Style - A technique that is utilized by continuously performing all the twelve styles in succession, which is noted to be the only effective method of killing Muzan Kibutsuji.

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.
 * The relationship between Yoriichi and Michikatsu parallels the mythology of the Shinto deities Amaterasu and Tsukuyomi, respectively. Amaterasu is the most sacred of Shinto deities, the sun goddess. Tsukuyomi, the moon god, is her former husband and brother. After Tsukuyomi killed Uke Mochi, another shinto deity, Amaterasu refused to ever look upon him again, moving to another part of the sky and beginning the cycle of day and night. Like the deities, the siblings also feud and have chosen different paths (that of the Demon Slayer and the Demon), developing their respective breaths of the sun and moon.

Quotes

 * (To Kokushibo) "My sympathies, my brother."
 * (To Sumiyoshi) "I am a man with no worth."
 * (To Kokushibo) "Brother your dream was to become the strongest samurai in the country, right? I want to be like you as well. I want to become the second strongest samurai in the country."