To activate Gear Fourth, Luffy bites into his forearm and inflates his muscular structure using his Gum-Gum Fruit's powers, specifically, he inflates his muscles bounded by Haki. This process significantly increases his size, muscle mass, and elasticity. The use of Haki, particularly Armament Haki (Busoshoku Haki), is crucial in this form, as it covers his body in a black, armor-like coating that increases his defense and the power of his attacks.
Gear Fourth has several forms, each tailored to different combat situations:
Boundman (Bounceman): The first revealed form, showcasing a massive increase in Luffy's size, with his body becoming more rounded and elastic. This form significantly enhances his power and speed, allowing him to bounce at high velocities and deliver devastating punches.
Tankman: A form that maximizes Luffy's defensive capabilities. It was first shown during his fight with Charlotte Cracker. In its "Full Version," Luffy becomes extremely large, using his increased mass and elasticity to absorb and redirect attacks.
Snakeman: A sleeker, faster form that Luffy used in his fight against Charlotte Katakuri. Snakeman enhances Luffy's speed and allows his arms to stretch and bend like snakes, making his attacks unpredictable and hard to dodge.
Gear Fourth significantly boosts Luffy's combat abilities, allowing him to take on formidable opponents who would otherwise be out of his league. However, it also has its drawbacks. The form consumes a tremendous amount of energy and Haki, limiting its duration. After Gear Fourth expires, Luffy is left in a weakened state, unable to use Haki for a certain period.
Despite these limitations, Gear Fourth is a testament to Luffy's growth as a fighter and his ingenuity in leveraging his abilities to face increasingly powerful foes. It represents a key milestone in his journey to become the Pirate King and stands as one of the most visually striking and powerful transformations in the "One Piece" series.
