From Viz:
Experience the origin story of Fire Fist Ace, the legendary older brother of Straw Hat Luffy, in this exciting manga by renowned artist Boichi! Adventure along with Ace as he gathers a ragtag crew of like-minded buccaneers, including Masked Deuce, Mihal, Skull, and the wild Kotatsu, and forms the Spade Pirates. Witness the power of the Devil Fruit as it bestows Fire Fist’s fearsome punching power. Piratical feats abound as Ace and his Spade Pirates head toward the New World and the dreaded Captain Whitebeard.

Based on both volumes of One Piece novel A (Novel). The manga has differences and omitted characters but features an original epilogue.

Including Boichi´s one-shots from the One Piece Cover Comic Project:

1. Roronoa Zoro Falls Into the Sea (Based on Chap 51-52)
2. Nami vs. Kalifa (Based on Chap 410-412)

Webcomic on Shonen Jump+