Marluxia and Larxene used Namine to manipulate Sora's memory, and were planning on using him to "take the Organization." But, Axel let Namine go, and shot that plan to hell.
So, what if their plan succeeded... to a point. Only, Larxene decides to betray Marluxia and tells Sora that he planned on hurting Namine. Sora destroys Marluxia, then Larxene manages to convince Xemnas to keep Sora and Namine around. Or, Marluxia catches Axel in the act, they fight, Axel destroys Marluxia, and Larxene abandons the plan to rebel.
This could lead to certain amusing incidents, like a meeting between Sora and Roxas. Or, if one wanted to, they could do something like making Sora Larxene's pet, for lack of a better word. Why wouldn't she want to have a pet Keybearer?
So, what if their plan succeeded... to a point. Only, Larxene decides to betray Marluxia and tells Sora that he planned on hurting Namine. Sora destroys Marluxia, then Larxene manages to convince Xemnas to keep Sora and Namine around. Or, Marluxia catches Axel in the act, they fight, Axel destroys Marluxia, and Larxene abandons the plan to rebel.
This could lead to certain amusing incidents, like a meeting between Sora and Roxas. Or, if one wanted to, they could do something like making Sora Larxene's pet, for lack of a better word. Why wouldn't she want to have a pet Keybearer?