Furthermore, this moment serves as a thematic inheritance from Gol D. Roger. While Luffy never met Roger, the awakening of the same power that the Pirate King possessed creates a lineage of spirit that transcends bloodlines. The Haki burst proves that Luffy carries the same potential to "turn this era upside down."
"Oda deliberately held back because Marineford is about Luffy’s failure, not his power-up. Giving him haki there would ruin the tragedy and the need for the timeskip." luffy conqueror haki in marineford episode
Luffy enters the war with the sole desire to save his brother, rejecting the politics of the Whitebeard Pirates and the Marines. His Haki manifests to protect Ace because his will is singular and uncorrupted by fear or doubt. This mirrors the "Supreme King" archetype found in the series—individuals who draw others to them and bend the world to their will. Furthermore, this moment serves as a thematic inheritance