Though his time in the series was brief, Rengoku’s influence on Tanjiro Kamado and his friends was profound.
His ultimate technique, Ninth Form: Purgatory , remains one of the most powerful and visually stunning displays of Flame Breathing in the franchise. If you'd like to dive deeper, I can: Detail the specific forms of Flame Breathing he used.
Tanjiro often recalls Rengoku’s words to stay resilient in the face of overwhelming odds.
His signature phrase, "Set your heart ablaze," serves as a core theme for the series, encouraging others to live with passion and move forward despite any despair.
His final message to his father eventually led Shinjuro to renounce his alcoholism and find redemption.