The Evolution of Nami's Boobs (One Piece) . man eating plants, a mermaid can grow up to be giantess as big as one of those sea monsters. r/OnePiece supports both manga and anime fans alike. considering Robin's grew as well and she was already a fully grown adult. Not that I. I can kinda buy Nami having a final growth spurt at the end of her teens. Her skimpy outfits kind of suit her personality and age too. I find Robin's.