This is Luffy's most impactful pre-timeskip Haki usage. On the execution platform, Ace is seconds away from being decapitated by marine executioners. Refusing to let his brother die, Luffy screams out in pure agony and rage.
Portgas D. Ace is on the execution platform, and the executioners raise their blades to end his life. Whitebeard is injured, and no one is close enough to stop them.
Frozen and dying from Magellan's venom in the frozen hell of Level 5, Luffy and Bon Kurei are surrounded by a pack of vicious, bloodthirsty military wolves.
While confronting the Flying Fish Riders, Duval’s massive pet bison, Motobaro, charges at Luffy. Subconsciously, Luffy glares at the beast, emitting a sudden pressure that terrifies the bison and causes it to faint. At this point, neither Luffy nor the crew understands what just happened. Episode 413: The Amazon Lily Arena
[Ep. 389] First Spark (Motobaro) │ [Ep. 413] Amazon Lily Arena │ [Ep. 438] Impel Down Wolf Pack │ [Ep. 478] The Marineford Blast Episode 389: The First Unconscious Spark