He didn’t speak. He didn’t need to. Every ounce of his being screamed one word:
A Marine captain raised a saber. Luffy ducked. A volley of cannonballs flew. He dodged. A wall of armored soldiers formed a shield wall. Luffy leapt. luffy haki in marineford episode
Whitebeard, gutted and dying, raised his bisento and roared to his remnants: "Protect Luffy!" He didn’t speak