Luffy developed this technique during his two-year training on the island of Rusukaina to combat the giant beasts that inhabited the land. It works by inflating his muscular structure rather than his bones (as in Gear 3) and coating his body in Armament Haki to maintain high-tension elasticity. Key Battles and Debut Instances Gomu Gomu no Mi/Gear 4 Techniques | One Piece Wiki
Below are the specific forms and the battles where they first appeared: Boundman (Bounce-Man) : First Appearance : Episode 726 / Chapter 784. Context : Luffy used this form to overpower Doflamingo after Gear 2 and Gear 3 proved insufficient.
: Luffy entered this form after consuming a massive amount of Cracker’s biscuits, turning his inflated body into a "tank" with high defensive capabilities. : First Appearance : Episode 870 / Chapter 894. when does luffy use gear 4
He will almost never open a fight with Gear 4 unless he knows the enemy is an Emperor-level threat (like Kaido). He typically exhausts Gears 2 and 3 first, testing the waters. If the enemy survives those barrages, or worse, brushes them off, Luffy calculates that the risk of the Haki exhaustion timer is worth the reward. He uses Gear 4 when losing the stamina gamble is preferable to losing the fight outright.
and even isolating the power to specific limbs ("Mini Gear 4") without a full-body transformation. Luffy developed this technique during his two-year training
It is vital to note that Luffy uses Gear 4 sparingly because of its massive drawback. Once the timer runs out, the Haki depletes, and Luffy is left unable to move for ten minutes. This tactical vulnerability dictates when he uses it.
Luffy first uses in Episode 726 of the One Piece anime, titled "Gear 4! The Phenomenal Boundman!". In the manga, the transformation debuts in Chapter 784 during the final stages of the Dressrosa Arc. Context : Luffy used this form to overpower
Luffy first debuts Gear 4 in the . Below is a definitive list of every arc and specific opponent where Luffy uses Gear 4, along with the trigger.