Yoriichi Tsugikuni, the most powerful demon slayer, had unparalleled abilities and invented Sun Breathing. Yoriichi's Demon Slayer Mark and Transparent World prowess made him unbeatable in battle.
500 years before the events of Demon Slayer, Muzan Kibutsuji escapes a gruesome death at the hands of Yoriichi Tsugikuni, the first Sun Breather and the inventor of all breathing styles.