In the popular anime series One Piece by author and illustrator Eiichiro Oda, Monkey D. Luffy learned to use Haki while training with former pirate king Gol D. Roger's right-hand man Silvers Rayleigh. This happened during the two-year timeskip in One Piece, between manga chapters 597 and 598, and anime episodes 516 and 517.
Haki is essential for survival in the New World of One Piece. It is an individual's ability to fight using a form of their spiritual energy. Haki has been around since the very beginning, though it was not always known by that name.
Disclaimer: This article contains spoilers from the One Piece manga.
Luffy learns to use Haki by training on Rusukaina Island in One Piece
Luffy's training under Rayleigh
After the war at Marineford in the One Piece series, the Straw Hat Pirates decided to train for the New World on separate islands. On Rusukaina Island, Luffy began his two-year-long training under the "Dark King" Rayleigh and learned about three types of Haki: Observation Haki, Armament Haki, and Conqueror's Haki.
Observation Haki improves a person's senses, Armament Haki is used to gain physical strength, whereas Conqueror's Haki is used to forcefully subjugate opponents or even leave them unconscious.
Rusukaina island was geographically important for Luffy to learn to control Haki because it had forty-eight seasons and around five hundred animals that were stronger than him. The harsh environment pushed Luffy to grow stronger.
Rayleigh first demonstrated all three types of Haki by combating a giant elephant, and then subjected Luffy to a series of tests, including blindfolding him to train his observation. Luffy then learned how to use all three types of Haki, particularly the rare Conqueror's Haki, which only a few people are born with.
Luffy had been using Haki unconsciously before, for example, when he knocked Iron Mask Duval's pet bison Motobaro unconscious, or when Ace was about to be executed by the Marines. However, he was unaware and untrained up until that point, and thus unable to use Haki at will.
The subsequent episodes show Luffy using Haki on his enemies: For example, he used Conqueror’s Haki in episode 518 of the anime to defeat Demalo Black.
Why Luffy needed to learn Haki
Luffy's training began immediately after he recovered both physically and psychologically from wounds received at the Marineford war in One Piece. Luffy needed to learn Haki in order to compete with the Haki-using pirates he encountered at Marineford.
While Luffy's Devil Fruit Gomu Gomu no Mi is not weak, it is also not the most powerful. Only Luffy's determination and creativity allowed him to come up with the gears that made him such a formidable opponent. But his limited understanding of Haki kept him from standing on the same level as the New World Pirates.
Thus, Luffy had to will himself to master Haki through rigorous training in order to protect his crew and fulfill his dream of becoming a pirate king by defeating the Emperors of the Sea and finding the One Piece.
Luffy's journey takes him to places where he keeps encountering and learning new things. With the incorporation of Advanced Haki and Awakening into the power system, a fighter's greatness is ultimately determined by their creativity.
Luffy has repeatedly proven himself to be a creative fighter who constantly learns, adapts, and optimizes. Learning to control Haki marked the beginning of a new chapter in Luffy's journey.