Luffy uses Haki unintentionally just as Ace is about to be executed. Luffy made a way through the execution platform with the help of Whitebeard Pirates and Allies, but Garp intervenes before Luffy can make it to the platform.
When Ace is about to be executed, Whitebeard tries to intervene but he is stopped because of the wounds he received. Much to the shock of the Commanders and Jinbe, Luffy uses his Haoushoku Haki unconsciously, preventing Ace from being executed because the executioners fainted. Many of the Marines also faint and even a few of the Whitebeard Pirates. Ivankov then asks Luffy how he gained that power, to which Luffy says he does not know. Rakuyo comments it's the Conqueror Haki. Aokiji is surprised and sweating a bit, and Kizaru said he was surprised in a sarcastic way.
Some of the Whitebeard Pirates say that Ace is alive and that the others fainted because of the burst of Haki from Luffy. They questioned if that was Ace's brother. Marines were seen knocked out and someone commented that they almost have passed out. Fossa then says that Luffy used Haki, just like Whitebeard and Shanks. Akainu commented that Luffy used his Haki unconsciously. Kizaru also commented on the tremendous power of Luffy. Garp comments that Luffy was born with it, as he had thought, and Ace comments, "he uses it too". Vice Admiral Doberman stated that those whose hearts are weak to back down, and that Luffy is not an ordinary rookie. He also commented on Luffy's Haki but that it's not surprising because he is the son of the RevolutionaryDragon. Ivankov then asks Luffy again how he obtained the power. Luffy is clueless as to what power he is referring to. Ivankov then comments that Luffy is not aware that he is using it, and therefore is not yet ready to use the power.
Whitebeard then orders his men to back Luffy up. The New World Captains fight against the vice admirals while the other pirates clear a straight path to the execution platform. Inazuma then reappears, having been hiding in Ivankov's hair, and uses his Devil Fruit powers to create a bridge that leads straight to the scaffold. Luffy runs up the path, but when he comes close to the platform, Garps jumps in front of him. Garp states that if Luffy wants to save Ace, he will have to kill Garp first.