“"Set your heart ablaze!" — the Flame Hashira who burned brightest, and went out on the Mugen Train.”
The Rengoku family's inherited breathing style — fast slashes overlaid with intense flame imagery, structured into nine forms.
The highest-power technique shown in the Akaza fight. The ninth form was self-developed by Rengoku — it did not exist in his father's notes.
Joy and duty fused into a single person. His unshakeable cheerfulness in any situation isn't a mask — it's genuine. He had completely merged his identity as a Pillar with his personal self, to the point where protecting the weak was how he overcame his own fear. He was himself until the very last moment.