Naminé is a very special Nobody. Born when Sora stabbed himself with the keyblade, she retains no memory of Kairi’s life or emotions. She came into existence in Castle Oblivion, where she was quickly discovered and imprisoned by the Organization members residing there. Marluxia and Larxene forced her to use her power to rearrange Sora’s memories and later she placed false memories into the Riku Replica. The idea was to create puppets to aid in their betrayal of the Organization. She’s jealous of his devotion to his friends, as she knows she has no one. This jealousy causes her to replace Kairi with herself in Sora’s heart. She also helped Riku as much as she could, and though she took Kairi’s form when speaking with him, she was surprised that he could tell they weren’t the same person.
Over the course of Sora’s trip through Castle Oblivion, Naminé is exposed to his sense of duty and valor as he fights for her, whom he believes to be his best friend. Both that and the kindness shown by the Replica towards her spark her sense of responsibility and she resolves to show herself to Sora and tell him the truth. She does so, though the Replica and Sora eventually battle over her, causing her to have to crush the Replica’s memories in order to spare Sora and save his life. Larxene notices this and torments Naminé over it, bringing about her downfall at Sora’s hands. With her conscience bugging her over what she’d done, Naminé began trying to fix Sora’s memories. Sora is completely forgiving of her, something that surprises her greatly. She admits that she can fix the damage, but Marluxia has to be defeated first. Being a hero type, Sora immediately runs off to do just that, allowing Marluxia to kidnap her while she’s watching the Replica.
Axel decides to take that moment to confront Marluxia about his traitorous behavior and Marluxia uses Naminé as a meat shield, surprising the girl terribly when Axel says he’s more than willing to kill her to get to Marluxia. Fortunately for her, Sora arrives then and distracts everyone, though he can’t stop Marluxia from disappearing with Naminé in tow. Later, when Sora again confronts Marluxia, the Nobody orders Naminé to erase Sora’s memories and destroy his heart. Realizing that this is a terrible order and one she cannot obey, Naminé refuses, causing Marluxia to threaten her life. Sora tells her to do it so it will save her life, but she’s fortunately stopped from having to make any further decisions by Replica’s arrival. Marluxia is defeated by Sora, Donald, and Goofy as the Replica guards Naminé.
Afterward, Naminé tells Sora he has a choice: to forget all about his past life, friends, and events or to forget about Castle Oblivion, all the events that happened there, and ultimately Naminé herself. Sora’s choice is to forget Castle Oblivion and while it deeply wounds Naminé on one level, she expected that choice and understands why he makes it. DiZ brought her, Sora, Donald, and Goofy to his lab in the Twilight Town mansion. There, the trio is put into stasis so Naminé can work her magic and sort out their true memories. She and Sora promise to meet again, this time as real friends.
She works tirelessly to restore Sora’s memories, but runs into a problem in Xion. Naminé is the one who realizes what Xion’s existence means: that Xion is holding some of Sora’s memories hostage and that Sora won’t wake up as long as Xion keeps them. After Xion meets Riku, he tells her to go talk to Naminé, and it is the blonde girl who tells Xion of her nature as a Replica, quite like the Riku Replica from Castle Oblivion. Naminé also informs Xion that should her “memories” return to Sora, she would disappear… literally. Everyone would forget her and it would be as though she’d never existed. Naminé is waiting for Xion’s answer when she’s pulled into Paixao…