Kyojuro Rengoku is the Flame Hashira in Demon Slayer Kimetsu no Yaiba, created by Koyoharu Gotouge. His Flame Breathing First Form Unknowing Fire is a high speed charging slash meant to decapitate a demon in one motion. Rengoku became especially iconic after Demon Slayer Mugen Train in 2020, and clips of his attacks and battle cries spread widely through anime edits, AMVs and soundboards. Fans still use this form callout to mark a fearless entrance, a last stand moment, or any scene that needs instant Hashira energy.