I think I was was born with special strength for the purpose of defeating Muzan Kibutsuji. But I was lacking. In the end, I failed. Because of that, many more people will die. And that pains me.
Yoriichi looked almost 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 nagagi with black hakama and a nichirin blade carried at the left side of his waist, conventional to most Demon Slayers. He sported the same hanafuda earrings created by his mother, passed down to Tanjiro Kamado from Tanjuro Kamado.
Yoriichi was a calm and respectful individual. He was extremely humble, seeing himself as just any other man and no one special; an example being the time he performed the Sun Breathing's forms for Suyako at her request and almost seemed embarrassed afterwards. 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 Breathing possessed, a generation would emerge that would further surpass their own. Generally, Yoriichi had a low and serene disposition, evident when he killed demons without changing expression or when Muzan was caught off guard by his immense skill because he appeared unassuming. But at the same time, he expresses strong emotions; he grieved the loss of Uta and their unborn child for ten straight days and was driven to tears seeing the joy Sumire showed at the simple act of being lifted up. He also expressed gratitude and thanked Sumiyoshi after his friend told him his life was not worthless and promised to preserve his Sun Breathing forms through his descendants.
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. Even 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 later 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.
Overall Abilities: Yoriichi is the strongest known character in the entire history of the series and the most powerful swordsman and Demon Slayer, being born with the Demon Slayer Mark and the Transparent 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 beyond compare. 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.
Demon Slayer Mark: Yoriichi is the progenitor of the 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, but maybe because he was the first one ever to have it and born with it naturally, unlike all other mark bearers who must trained using Breathing Technique to attain it.
- Bright Red Nichirin Blade: Yoriichi is the first person ever to be able to turn his Nichirin Blade into Bright Red color as he was born with the ability. When fighting, Yoriichi can dye his black sword to bright red at will, letting him hamper the enhanced regeneration of Demons, even Muzan's nigh-absolute regeneration, leaving permanent damage burned into his cells that haven't healed for hundreds of years.
- Transparent World: Yoriichi harbors the ability to use the Transparent World since birth, which made him suspect that he was gifted with this ability to defeat Muzan Kibutsuji as this ability perfectly counters his advantage of having multiple organs as Yoriichi can perceive them and target them to kill him easily.
Immeasurable Speed & Reflexes: Yoriichi possessed godlike levels of speed which on par, if not surpassed that of the Demon King, with which he was able to dodge every attack that Muzan launched at him and near-fatally injure Muzan with one move, despite the Demon's own immeasurable 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 300 in only seconds. Later, when Yoriichi was in his 80s he still can move fast enough to slit Kokushibo's throat without the latter being able to even draw his sword out of sheath to counter Yoriichi's attack, despite him being on guard and Yoriichi's blade was slightly near his throat.
Immeasurable Stamina & Endurance: Even as a child, Yoriichi could run for days on end without rest, he even remarked he didn't feel the least bit enervated. As Yoriichi managed to survive all the way to his 80's without his body succumbing to his Demon Slayer Mark or him having lost any of his original strength despite his advanced age and blindness, its likely that Yoriichi possess immense superhuman durability and endurance to still be fully capable of fighting and killing demon despite already being an aged old man without his power waning.
Immeasurable Strength: As the most gifted individual, Yoriichi possesses a caliber of strength unseen of before. As a child, he could knock out a grown man with inclined physical talent with a wooden blade, even causing extremely severe bruises. When he was an adult, he fought and slice off the head of Muzan Kibutsuji, the most fortified body part of the strongest demon in existence with the perfected Thireenth Form of the Sun Breathing.
Selfless State (
Tactical Intellect: As a child prodigy, Yoriichi possesses above average mental capabilities. Despite not speaking for most of his childhood, his first words were very clear and pronounced. He also displayed maturity beyond his age by helping and noticing her mother's illness. As another testament to his mental capabilities, he has incredible concentration abilities and wits. With an arsenal of techniques at his disposal, Yoriichi has to be really decisive and sagacious when using them.
Unparalleled Swordsman: Yoriichi was the greatest swordsman in all of history. Even as a 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 modelled after him had to be made with 6 arms wielding katanas and utilizing 108 techniques to even attempt to imitate Yoriichi's skills, and even then the doll was vastly inferior compared to him. His swordsmanship easily overwhelmed the Demon King, Muzan Kibutsuji and he would have ended his twin brother, Kokushibo, if he didn't die of old age.
- Clear Blue Sky (
碧 羅の 天Heki-ra no Ten?, lit. "Azure Heaven") - The user spins their body vertically to deliver a 360° slash.
- Raging Sun (
烈 日 紅 鏡Retsujitsu Kōkyō?, lit. "Scorching Crimson Mirror") - The user unleashes two horizontal slashes to hit or defend from incoming attacks.
- Burning Bones, Summer Sun (
灼 骨 炎 陽Shakkotsu En'yō?, lit. "Bone Burning Sun") - The user unleashes a large circular slash that defends from imminent frontal attacks.
- Setting Sun Transformation: (
斜 陽 転 身Shayō Tenshin?, lit. "The Setting Sun") The user backflips into the air to deliver a powerful upended sword slash.
- Solar Heat Haze (
飛 輪 陽 炎Hirin Kagerō?, lit. "Soaring Flame Haze") - The user charges towards the target, unleashing a horizontal slash seemingly covered in haze that fails to land, but actually does hit the target.
- Beneficent Radiance (
輝 輝 恩 光Kiki Onkō?, lit. "Shining Ray Of Grace") - The user spirals into the air and delivers a powerful slash that surrounds the enemy.
- Sunflower Thrust (
陽 華 突Yōkatotsu?, lit. "Sunflower Lance") - The user unleashes a single thrust attack with the point of the blade.
- Dragon Sun Halo Head Dance (
日 暈の 龍・ 頭 舞い Nichiun no Ryū Kaburimai?, lit. "Solar Halo Dragon Dance") - The user unleashes a continuous fast and powerful sword attack that seemingly takes the form of a flaming sun dragon. This technique is capable of decapitating multiple enemies at once.
- Fire Wheel (
火 車Kasha?, lit. "Fire Chariot") - The user leaps behind the opponent and spins in the air downward, releasing a sword attack in a circular motion.
- Fake Rainbow (
幻 日 虹Gen'nichi Kō?, lit. "Parhelion Rainbow") - The user performs high-speed twists and rotations, thus creating afterimages used mostly to evade attacks. The afterimages work most effectively on enemies with good vision.
- Flame Dance (
炎 舞Enbu?, lit. "Flame Waltz") - A two-combo strike which starts with a vertical slash and then a horizontal one right after.
- Thirteenth Form (
拾 参ノ 型Jū San no kata?) - The user continuously performs all twelve forms of Sun Breathing in repetitive succession to increase the accuracy and agility of his movements while reducing fatigue. This form was created solely for the purpose of killing Muzan, since the repetition of all twelve forms aims to destroy Muzan's twelve vital organs (seven hearts and five brains) that move freely inside his body thanks to his shape-shifting ability.
Standard Nichirin Katana: Yoriichi harbors a standard Nichirin Blade that is usually a deep shade of black, but when engaging in combat, it turns a crimson red. His katana's hilt is circular shaped with 4 slight indentations, with a black center and a golden border. Yoriichi's katana also has the words Destroy Demons (
- Yoriichi's family name is composed of the kanji for "to inherit, succeed" (継 tsugi?) and "country" (国 kuni?), while his first name means "destiny" (縁 yori?) and a variation of the kanji for "one" (壱 ichi?).
- 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 breathings of the sun and moon.
- Yoriichi's first words to his family were "I can hear you" as they believed he was deaf, up until that point.
- It is hinted that he and his wife reincarnated in the future as a very happy couple with kids.
- (To Kokushibo) "My sympathies, my brother."
- (To Sumiyoshi) "Sumiyoshi... those who master their trade all arrive at the same place. Even if the times change or the way to that place changes they are certain to reach the same place. You seem to think I'm someone that's special...But I'm not. I cannot protect anything that's important to me... and I was unable to accomplish even one thing that I should have in this life. I am a man without any value."
- (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."
- (To Sumiyoshi) "I think I was was born with special strength for the purpose of defeating Muzan Kibutsuji. But I was lacking. In the end, I failed. Because of that, many more people will die. And that pains me."
- (To Muzan) "What is the value of a life to you?"