Yuffie

Yuffie Kisaragi is a character from Final Fantasy who makes an appearance in all Kingdom Hearts games. She travels with Leon.

Kingdom Hearts
Yuffie is met in Traverse Town. Sora mistakes her for Kairi. She and Leon tell Sora the Keyblade. She retreats from the room when a Soldier Heartless attacks.

Kingdom Hearts: Chain of Memories
Like all of the Traverse Town characters, she does not remember Sora, but still knows his name.

Kingdom Hearts 2
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.