I recommend One Piece: Caesar to you. The main character of the book is a barbarian, the same name as the male protagonist Caesar you mentioned. The novel is also a comprehensive comic novel, involving many anime characters. The timeline that the male protagonist knew about was until Luffy completely defeated the " Hundred Beasts " Kaido. He was a double fruit ability user and could transform into a dragon. There are also keywords in the book such as One Piece, hegemony, decisive killing, etc. I believe you will like the plot of this novel. I hope you like my recommendation.