A unique Nobody who has the powers to alter Sora's memories and those he has connections with.
Chain of Memories
Namine first appeared in Kingdom Hearts: Chain of Memories as a hostage of Organization XIII, at the time Sora was in Castle Oblivion losing his memories slowly. Eventually Axel freed her and she was able to return most of Sora's memories, those except his adventure in Castle Oblivion. This took a year to complete, while Sora was sleeping.
Namine writing in her notebook
Kingdom Hearts II
In this game Namine has less screen time but still plays an important role. Nearly finishing piecing Sora's memories together she desired to see Roxas, this would led to Roxas learning more about his true self. She isn't seen much until the final cutscenes. After a major portion of the game Namine returns to help Kairi escape from the Oganization's stronghold. Then the truth is revealed, Namine is Kairi's nobody when Sora unlocked his heart with a Keyblade. At the end the two merge together becoming whole.