@alenj2j So Harry is four years old when he arrives on the One Piece world. How many years has passed since Luffy become pirate king?..I am going to guess he already defeated the World Government as well. But how would Harry return to his home wotld?. Just a little suggestion for how Harry can appeared. It can be when Luffy meets Hancock for the first time and Harry pops up like nothing baldy beaten (courtesy of his uncle). Now how would Hancock react to that?.. Considering she probably had a similar fate when she was a slave. Now, about Harry eating the Yami Yami no mi and Robin being a history teacher sounds nice and poor Draco can have a heart attack of he provoked Robin. Also, as we don't know how much time passes between going to Fishman island and Egghead, you could skip after that, explaining only in flashbacks..What do you think?.