which episode luffy use gear 4

Luffy first uses Gear 4 in One Piece anime episode 726, titled "Gear 4! The Phenomenal Boundman!" This episode originally aired on January 17, 2016. In this episode, Luffy activates Gear 4 during his battle with Donquixote Doflamingo in the Dressrosa Arc, dramatically increasing his strength, speed, and durability to gain the upper hand in the fight.