One Piece – Halfway Broken

When a young Monkey D. Luffy ends up braindead after an accident while training with his grandfather, someone else who wasn't supposed to die is given a second chance. Alex, a 17-year old teenager from earth wakes up as Monkey D. Luffy, with a floating textbox declaring him a Gamer. (Not an SI story, Different DF for Luffy, Expanded Crew, Check first chapter for more details) — Description from novelcodex.org