Robin's Past! The Girl was called a Devil!

Twenty years into the past, Robin is growing up on the island of Ohara. Her aunt, with whom she lives while her mother is away doing research, treats her poorly. Other children ostracize her. Studying in the world's greatest library, the Tree of Omniscience, in the hopes of being allowed to help the local archeologists in their forbidden research, Robin earns the rank of a scholar in archaeology at age eight. However, when she announces her intention to help, her request is denied because of her youth. Disappointed at being rejected again, she walks along the shore, where she stumbles on Jaguar D. Saul, a giant and deserted vice-admiral of the navy. The two become friends and Saul teaches her to laugh.