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 ...

Oda shares a hypothetical scenario where Sabo saves Ace at Marineford, but it's considered a dream by Luffy and Sabo ... Being an amazing war arc that uses the expansive cast and world of One ...