Yoriichi Tsugikuni is a major supporting character in Demon Slayer: Kimetsu no Yaiba. He is a legendary Demon Slayer who lived nearly 500 years ago during the Sengoku era (the Golden Age of Demon Slayers), as well as the strongest Demon Slayer to have ever existed. He is also the inventor of Breathing Styles, being the one who created the first ever Breathing Style that would eventually become the Hinokami Kagura used by Tanjiro Kamado and members of the Kamado Family. Yoriichi is the younger twin brother of Michikatsu Tsugikuni, who later became a demon and joined the Twelve Kizuki. Yoriichi is a tall man with a muscular build, fair skin, maroon eyes, and long spiky hair with red tips that he kept in a ponytail. He has a similar overall appearance to his twin brother Michikatsu, but unlike him, he was slightly more slender, had shorter bangs, and wavier hair than him. Yoriichi is always seen with an aloof and solemn look on his face, rarely showing emotion. Yoriichi wore a red haori over a very pale orange-colored nagagi kimono with a black umanori-styled hakama, a pair of zōri with red straps and white tabi socks, with a Nichirin Sword carried at the left side of his waist, conventional to most Demon Slayers. He sported hanafuda earrings created by his mother as charms when he was thought to be deaf; he later gave them to his friend Sumiyoshi, who then passed the earrings down to his descendants and eventually Tanjiro as well. Yoriichi was a calm and respectful individual who wore a solemn and reserved expression at all times, rarely showing outbreaks of emotion. Generally, Yoriichi had a matching low and serene disposition, evident when he killed demons without changing expression or when Muzan was caught offguard by his immense skill because he appeared unassuming. Because of his gentle disposition and unchanging facial expression, most could not tell what he was feeling: the only person who could read his feelings without difficulty was his wife Uta. He was also extremely humble, seeing himself as just another man and no one special despite his extraordinary abilities; 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 immense power of the Demon Slayers after they started using Breathing Styles, a generation would emerge that would surpass their own. Despite appearing mostly nonchalant, he experiences emotions like any other person; 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 smiled warmly and expressed gratitude to Sumiyoshi after his friend told him his life was not worthless and promised to preserve his Sun Breathing forms through his descendants. Yoriichi is also very kind, shown when he was on the way to fetch a midwife in preparation of the birth of his child, only to stop and help an old man he met along the way reach his dying son. As a child, Yoriichi looks up to his older brother Michikatsu. Michikatsu's dream is to become the strongest samurai in the land, so he said that he would become the second strongest. Even in his childhood, he was extremely reserved and quiet, even being believed to be deaf by his family for seven years as he never spoke. Yoriichi cared for his ailing mother when no one else knew she was ill and protected his father by not telling anyone about how he berated him as a child, even when his father did not love him. He respected his older twin brother and he kept the flute Michikatsu gave him before he left home all the way till his death. When he met him after sixty years, the latter having embraced his new life as a demon. Yoriichi was deeply devastated by what his brother had become and cried. Nonetheless, he attempted to kill Michikatsu in order to stop him as a traitor to the Demon Slayer Corps.