One Piece: Initially tricked into joining the Marines by Garp

Having transmigrated into the world of One Piece, Rorschach found himself all alone. Just as he was becoming disheartened, he unexpectedly awakened a dimensional synthesis system. The system's first task was to survive on a deserted island for a year. This task immediately hit Rorschach hard. However, after some trial and error, Rorschach surprisingly learned how to make senbei (rice crackers) by hand. A year later, a warship with a dog's head on its prow passed by the island and happened to see Rorschach, who could unleash fiery flying slashes. Garp immediately took a liking to his talent and, after some persuasion, managed to get Rorschach onto his ship. ...