Yoriichi Tsugikuni is a major supporting character of 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 progenitor of Breathing Styles, being the one who created Sun Breathing.

Yoriichi is the younger twin brother of Michikatsu Tsugikuni, who later became a demon and joined the Twelve Kizuki.

Like his twin brother, Yoriichi is a tall and muscular man with long and spiky hair with red tips that he kept in a ponytail. However, unlike him he was slightly more slender and had shorter bangs and wavier hair than his brother. His Demon Slayer Mark was at the same place at the top of his forehead as Tanjiro, albeit lighter in color. Yoriichi is always seen with a solemn and calm look on his face, rarely showing emotion.