Guy's father taught him when he was a child how to open the Eight Gates, what Duy called the only thing he'd learned during his decades of training that was worth passing to Guy. With each gate he opens, Guy's physical speed, strength, and chakra levels increase; with each gate he opens, his body also takes more and more damage, with the opening of all eight gates causing eventual death. For this reason, Duy stipulated that the Eight Gates were only to be opened in order to protect something or someone precious, a philosophy Guy follows and that he also requires of Lee. Guy has been shown enduring the rigors caused by the gates for periods of time after using them, but inevitably he succumbs to the pain or exhaustion they cause.
Guy has created several different jutsu that he can perform once certain gates have been opened: with the first gate, he can use the pile-driving Front Lotus; with the third gate, he overwhelms opponents with punches through the Reverse Lotus; with the sixth gate, Guy produces a series of rapid punches that ignite his hands through air friction, what he calls Morning Peacock; with the seventh gate, he launches concentrated air pressure at opponents that violently expands on contact, creating what he calls his one-hit kill move, the Daytime Tiger; with the eighth gate, his punches create shock-waves of such power and range that he doesn't even need to make contact with his opponent, what Guy calls Evening Elephant; also with the eighth gate, he has Night Guy, a single kick that is so fast that it distorts the space around him.