Name: Silvers Arthur "The Scarlet King"
Age: Same as Ace
Race: Human
Weapon: Longsword(Ruined King)
Cheat: Yoriichi Tsugikuni's Talent added to his own potential
Yoriichi was the strongest Demon Slayer in history, being born with the Demon Slayer Mark, access to the Transparent World, and Selfless State, as well as possessing a physique polished to the highest caliber and innate swordsmanship talent. As a seven-year-old child who had never picked up a sword before, he was able to defeat a trained sword instructor effortlessly, and he was referred to as a miraculous prodigy beyond compare. After training as a Demon Slayer, Yoriichi could defeat multiple demons to the point that 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 overpowered him in an instant, having him on the verge of death until he barely managed to escape. Despite having avoided death, Muzan was deeply scarred by that encounter, referring to him as the true "monster" between the two of them, and even the sight of his earrings made him tremble in shock, while mere memories of Yoriichi caused other demons to tremble in fear despite having never seen him before.
Shortly before his death of at least 85 years, he battled Michikatsu, now a demon by the name of Kokushibo and holder of the title of Upper Rank One. Despite his advanced age, he quickly gained the upper-hand in the battle with a single move, 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 that Yoriichi's power was still in his prime.
Genius Intellect: As a child prodigy, Yoriichi was extremely intelligent. Despite not speaking for most of his childhood, his first words were very clear and pronounced. He also displayed maturity beyond his age as he noticed her mother's illness and helped her all the way till her death. As another testament to his keen intellect, he could immediately use the Transparent World in combat despite never fighting before, being able to intuitively determine out that the lungs of a person will expand before they attack and that he needed to watch their bone movement, muscle contraction, and blood flow, which he used to his advantage instantly in the midst of battle.
Even with just the knowledge of how to hold a sword properly and go into a stance, he was able to instantly overpower a trained sword instructor, causing him to go unconscious and inflicting many injuries all over his body. His unique intellect brought about the "Golden Age of the Demon Slayers" as he invented the Breathing Styles and modified the original Breathing Technique to suit the abilities and individual strengths of others. Furthermore, he was able to surmise that Muzan's weaknesses were his seven hearts and five brains and created an entirely new technique in that split second to overwhelm him.
Demon Slayer Mark: Yoriichi was the progenitor of the Demon Slayer Mark, having been born with it and possessing the tremendous physical abilities granted by its effects all throughout his lifespan. Unlike all other users of the Mark in his era, which cursed them to die before the age of 25, 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 it is presumably because he was born with it, unlike other Demon Slayers who have to obtain it themselves.
Selfless State: During their confrontation, Muzan noted that Yoriichi emanated absolutely no sense of drive, hatred, anger, fighting spirit, animosity or even bloodlust despite being in the midst of a battle against him, rendering it practically impossible for Muzan to detect him, predict his movements, or gauge how powerful he was with his senses. This gave Yoriichi an edge in battle against Muzan when he underestimated his strength, a mistake that haunted the Demon King for the rest of his life.
Physical Abilities
Immeasurable Speed & Reflexes: Yoriichi possessed unparalleled levels of speed that surpasses all other characters in the series, including that of the Demon King, shown when 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. Even when Muzan divided himself into 1,800 flesh pieces to escape, Yoriichi still managed to reduce the number down to 300 in mere moments.
Even on the last day of his life, he was able to easily blitz Kokushibo, Muzan's strongest subordinate, slitting his throat almost instantly despite Yoriichi telling him when he would strike. As another testament to his godlike movement speed, Yoriichi Type Zero, the robot doll modeled after him used by Demon Slayers to train, was built with six arms because two arms alone couldn't replicate Yoriichi's movements.
Immeasurable Stamina & Endurance: Even as a seven-year-old child, Yoriichi could run for a whole day without rest; he even remarked that he didn't feel the least bit enervated. His vitality was also beyond the level of any human, being able to survive without food or water for ten whole days while embracing his dead wife. Moreover, Yoriichi lived to his 80s without his power waning in the slightest, as shown when he instantly outmatched Kokushibo during their final confrontation.
Immeasurable Strength: Yoriichi possessed tremendous levels of physical strength, possibly beyond that of nearly all other Demon Slayers in existence. As a child, he could knock out a grown man with inclined physical abilities with a wooden blade, even causing extremely severe bruises the size of fists. When he was an adult, he was able to effortlessly slice off the neck of Muzan Kibutsuji, the most fortified body part of the strongest demon in existence.
Extrasensory Perception: Outside of the sixth sense granted by the Transparent World which allowed him to see the inner workings of a person, Yoriichi also had extremely honed sensory abilities, able to detect things outside the normal range of perception. Like most high-level Demon Slayers, Yoriichi would be able to discern the aura of demons from humans while also be able to tell the strength of his enemies at a glance. During Yoriichi's first encounter with Muzan, he could immediately tell that, by destiny, he was born into this world to defeat him. Yoriichi was also able to accurately sense the Demon King's aura, which he describes as magma erupting from a volcano.
Unparalleled Swordsmanship: Yoriichi was the greatest swordsman to have ever lived. Even as a seven-year-old child with no training, he was capable of easily defeating a trained swordsman the very first time he ever picked up a sword, striking him in multiple areas across his body faster than the eye can process. 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 still vastly inferior compared to him. His swordsmanship easily overwhelmed the Demon King, Muzan Kibutsuji and he would have killed his twin brother, Kokushibo, the strongest swordsman in the current era, had he not died of old age.