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. Yoriichi is the younger twin brother of Michikatsu Tsugikuni. Yoriichi is always seen with an aloof and solemn look on his face.