Kuina was Zoro’s childhood friend and number one rival. Even as a child, Zoro was strong enough to defeat most adults, but couldn’t defeat Kuina(losing 2001 straight matches). Zoro aspired to be just as strong as she was. After their 2001st duel, Kuina admitted that, because she was a girl, she believed that as their bodies matured she would one day inevitably lose to Zoro in strength, even though she, like Zoro, dearly wanted to become the world’s best. Zoro was annoyed that if he one day surpassed her, she would believe that it was because of her body and not his strength. He made a promise with her that someday one of them would become the world’s greatest swordsman. She died soon after in an accident.
Zoro holds his vow to Kuina dearly and, whenever he comes close to death (such as during the events with Morgan and Dracule Mihawk), he recalls his memory of her to spur him on. He currently wields her sword, Wado Ichimonji, and intends to achieve their dream to fulfill his promise to her.