One Piece reasserted itself as a highly relevant Big Three shonen series with the debut of Gear 5, Luffy's newest combat form. This represented a major turning point in many ways, from the reveal of the Gum-Gum Fruit's true nature to giving Luffy a real chance to defeat one of the Four Emperors. It's also an example of personal growth and revelations for Luffy, changing him on the inside.
Source：https://www.cbr.com/one-piece-luffy-gear-5-laugh-meaning/
