Larxene was plotting against the Organization with Marluxia, but she falls into Axel's trap. He suspects that there are traitors, so he mentions their plans, pretending to be one of them. Larxene naively thinks that he is part of it too, thus admitting her treachery. They get along pretty well, mostly because Axel is pretending to be on her side rather than the Organization's. In the end Axel brings justice and uses Namine to help bring about Larxene's end at the hands of Sora.