Yuffie

Yuffie Kisaragi is a character from the Final Fantasy VII series who makes an appearance in all Kingdom Hearts games. She travels with Leon, whom she mostly refered to by his real name sometimes to his annoyance. She ocassionly refers to herself as the "Great Ninja Yuffie", weilding a large wind-blade shuriken as her weapon.

Kingdom Hearts
Yuffie is met in Traverse Town, with a groggy Sora mistaking her for Kairi. She and Leon told Sora all about the Keyblade. She retreats from the room when a Soldier Heartless attacks.

Kingdom Hearts: Chain of Memories
Modeled after the real Yuffie based on Sora's memories.

Kingdom Hearts II
Yuffie is a member of the Hollow Bastion Restoration Commitee. She explains the town's defense system and fights alongside the others during the Heartless invasion.

Trivia

 * Yuffie was used instead of Rikku, as she was involved in FFX-2 at the time. But traces of Rikku's intended attire remain on Yuffie during Kingdom Hearts and Chain of Memories. By Kingdom Hearts 2, Yuffie wore the clothing she had on FF7: Advent Children.
 * In the Japanese version, Yuffie was voiced by popular seiyuu Yumi Kakazu, whose other involvements with SquareEnix besides voicing Yuffie in the FF7 series was to voice Ritz of Final Fantasy Tactics Advance radio-drama and Lyra(Dante) in Fullmetal Alchemist. In the English version of Kingdom Hearts, Yuffie was voiced by Christy Romano, who voiced Yuffie in Advent Children starred in Disney shows like Even Steven and was the title character of Kim Possible. In the English version of Kingdom Hearts 2, however, Yuffie was voiced by Mae Whitman while she voiced her in Dirge of Cerberus. whose last involvement with Halery Joel Osment was as Shanti and was the voice of Rose on American Dragon: Jake Long.