Gear — Fourth One Piece

: Initially, this form had a strict time limit (roughly 20 minutes). Once it expires, Luffy is left exhausted and unable to use Haki for 10 minutes , leaving him extremely vulnerable.

Luffy inflates his muscular structure rather than his bones or blood vessels. But the key ingredient is . By coating his inflated muscles in Haki, he creates a structure that is paradoxically bouncy yet incredibly durable. He describes it as a "Rubber Man" becoming a "Rubber Balloon," but one that hits like a cannonball. gear fourth one piece

Unlike Gear Third, which made Luffy slow and vulnerable, Gear Fourth maintains high mobility. The compression of the rubber allows him to retract his limbs into his body and snap them back out with terrifying velocity. : Initially, this form had a strict time

This technique combines the air-injection properties of Gear 3 with the blood-flow acceleration of Gear 2, all while heavily utilizing to coat and harden his inflated muscles. By blowing air directly into his muscle structure, Luffy achieves a unique state where his body is simultaneously hard as iron yet incredibly elastic. Main Variations of Gear Fourth But the key ingredient is

When Luffy faced Charlotte Katakuri, raw power wasn't enough. He needed speed, and he needed unpredictability. Enter .

Furthermore, Gear Fourth serves as the ultimate rebuttal to the series’ recurring villains. Doflamingo’s “Parasite” strings control people, robbing them of free will. Kaido’s brute force crushes spirits into submission. Against such world-breaking power, simple speed or strength is insufficient. Luffy needs a technique that embodies overwhelming, crushing liberation . The “King Kong Gun”—a fist the size of a house, compressed and released—is not a punch; it is a declaration that no chain, string, or scale can bind a truly free will. By sacrificing his sleek silhouette for a hulking, tyrannical form, Luffy symbolically becomes the monster necessary to slay other monsters. He does not enjoy this form; he endures it. The strained veins, the constant Haki drain, and the eventual collapse all suggest that Luffy hates this side of himself. But he uses it because the freedom of his friends is worth the temporary loss of his own.