Naminé Was born when Sora stabbed himself with Ansem's(Xehanort's heartless') keyblade, when he restored kairi's heart. Naminé's a very odd Nobody as she was born from Kairi's heart and Sora's body and soul. Kairi's own body never became a Nobody because she was one of the Princesses of Heart so her body and soul were never able to leave the Realm of Light. This means that Naminé was born without Kairi's memories,which continues to make her more and more unusual. Because of the fact that Naminé is formed from Sora's body, she has the power to manipulate his memories as well as the memories of those who are connected to him such as kairi's. Like Roxas, Naminé seems to possess true emotions, being a special Nobody. While most Nobodies pretend to have emotions by acting on the memories of their past lives in order to react to a specific situation, Roxas and Naminé had no memories of their past lives, and thus had no basis for any acting; presumably, this is because their original selves (a Keyblade Master of the Realm of Light and a Princess of Heart) still exist due to the unusual nature of their births. There you go haha. :)
