One Piece focuses heavily on the "found family" trope, most of all with the Straw Hat pirates and the Luffy/Ace/Sabo brother trio. The story doesn't linger much on Luffy's biological family, however. It wasn't until the end of the Water 7/Enies Lobby saga that readers finally learned a bit about Luffy's family through his grandfather, Monkey D. Garp.
Source：https://www.cbr.com/one-piece-luffy-grandfather-origin/
