One Piece - episode 35 - 01 Aug, 2000

Nojiko starts her story about Nami's childhood and their adopted mother, Bellemere, a former Marine. After a bloody battle in a small village between pirates and Marines that left her the only apparent survivor from both sides, Bellemere finds a toddler Nojiko holding a infant Nami. Taking the girls back to her home Cocoyashi, Bellemere decides to adopt Nami and Nojiko. Despite being poor and none of them being related by blood, they had a happy life. It is shown that as a child Nami was a prodigy in cartography (the study and making of maps and charts) and navigation. (Source: Wikipedia) East Blue saga: Arlong Park arc: (5/14)