Kuina is Zoro's childhood friend and number one rival. They both promised to be the greatest sword fighters in the world, but tragically she died at a young age.
Kuina was the daughter of the dojo leader in Frost Moon Village, Koshiro. She trained relentless in her father's dojo and was the most skillful fighter. Kuina was skilled enough to challenge any adult.
Kunia is a supporting character in the One Piece series that was created by Eiichiro Oda. The series first began serialization in Weekly Shōnen Jump on August 4, 1997. She only appears in flashbacks becasue she passed away before the original events of One Piece.
Her first appearance was in One Piece Volume 1 CH. 5 "The King of the Pirates and the Master Swordsman", and her first anime appearance was in One Piece - Episode 2 "Enter the Great Swordsman! Pirate Hunter Roronoa Zoro". Her character in the Japanese series is voiced by Machiko Toyoshima, and the U.S. dub produced by FUNimation is performed by Monica Rial.
Kuina's name comes from the name of a flightless bird called the Okinawa Rail (山原水鶏, Yanbaru Kuina). This reflects her frustration of not being able to reach her dream. However, Oda has stated, "Though a bird cannot fly, it does not mean it never will.".
Zoro Roronoa had come to the dojo as a young boy in order the challenge the strongest fighter. Koshiro offered the challenge of his own daughter. Zoro was younger and much smaller. She defeated him, and he stayed to train in hopes of winning over her.
One night Kuina over heard her father talking about giving the dojo over to Zoro. She burst in the room, upset, demanding to know why he wouldn't believe in her. Her father told her that girls can't be as strong of a sword fighter as a man. This broke her heart. She declared she would be the greatest sword fighter of them all and ran. Despite her declaration she was in tears.
Zoro challenged Kuina to another match in the moonlight and with real swords. She used her personal meitou katana the Wado Ichimonji. He was devastated that no matter how hard he trained he can't catch up to her. She told Zoro he was lucky to be a boy. That as a girl she would become weaker. This enraged the young Zoro. He refused to believe such a thing and made a promise with Kuina. That they would both become the greatest sword fighters in the world and fight again to finally decide who was the best. These honest words lifted her heart and she agreed, but couldn't help teasing him that he will always be weaker then her.
Kuina was training even harder than ever. The anger and dedication she was showing was even starting to impress her father. Though, tragedy of the worse kind fell upon the dojo. In one simple accident, Kuina fell down the stairs and died from her injuries. Zoro was the most devastated by this loss. They would never get the chance to fulfill their promise together to reach the top.