Luffy this Haki at Marineford. He unleashed it unconsciously under extreme emotional stress. The first time he intentionally uses Conqueror’s Haki is in the Post-War Arc (Episode 517, against the fake Straw Hats on Sabaody).
A wave of invisible pressure burst from Luffy. The executioners—two grown men trained for war—dropped instantly, unconscious before they hit the ground. The fighting below momentarily paused. The air grew heavy. luffy conqueror's haki marineford episode
It wasn't a new Gear transformation. It wasn't a final attack. It was a split-second pulse of energy that changed how the world—and the audience—viewed Monkey D. Luffy. Luffy this Haki at Marineford