Luffy started getting a grip on Observation Haki during the two-year time skip after the Marineford chaos. He trained with Silvers Rayleigh on Rusukaina Island, a brutal place with wild weather ...

This article contains spoilers from One Piece's Elbaf Arc. Not all powerful Haki users in One Piece hold captain titles, like Katakuri, Ben Beckman, and Rayleigh. Strong Haki users like Kuzan ...