Hyakkimaru is a young man who lacks 48 body parts because they were taken from him by demons before birth, which was promised by his father, Kagemitsu Daigo to obtain his wish to take over the country. When the baby boy was born, he was missing 48 parts of his body, and thus was abandoned, thrown into a river. Hyakkimaru has grown up and now has obtained fake body parts so he can eliminate the 48 demons that were made from his body, to retrieve his missing body parts. Along for the adventure is the boy thief, Dororo, that he becomes friends with.
Summary taken from: MyAnimeList