It has multiple variations that enhance some amount of the user's defense, speed, and power beyond their normal limits. Luffy coats his arm in Armament Haki before biting into his forearm. Similar to how he activates Gear 3, he blows an incredible amount of air into his body, but this time he inflates his muscular structure before distributing the air throughout his body, with emphasis on his upper half and he also gains a tattoo-like design on his body made of Haki.
When utilizing Gear 4, Luffy makes extensive usage of his Armament Haki by coating his arms, legs and much of his torso in it to the point that they turn black from hardening. The Haki coating across his body resembles the wispy ends made from flames, giving it the appearance of tattoos, and he gains shading around the inner and outer edges of his eyes, along with his irises turning brown.
He also physically grows taller, standing around 4 meters tall. Similar to when using Gear 2, Luffy emits a stream of steam that resembles the flame collars on Awakened Zoan users. Combined with Luffy's rubbery composition and his compressed muscle structure, Gear 4 both adds explosive power to Luffy's attacks and grants him enhanced defensive capabilities far beyond what he can demonstrate with or without Gear 2 or Gear 3.
While Luffy is using Gear 4, his physical strength and speed are increased to the point where he is able to overwhelm a Warlord of the Sea , Donquixote Doflamingo, and the second strongest member of an Emperor 's crew, Charlotte Katakuri , whereas before, Gear 2's lack of strength and Gear 3's lack of speed made them ineffective in the fight.
Unlike the previous forms, Gear 4 focuses on compression more than stretching in a manner similar to the Bane Bane no Mi.
