I wonder what mission Axel, Xion, and Xigbar had in Wonderland? I imagine before they fight, the three of them are drinking tea together since they are in the Mad Hatter room. They are drinking tea, Xigbar says something that shouldn't be heard by child ears, and then Xion proceeds to knock him out in of pure disgust, give the middle finger to the Organization and leave. At least that's my headcanon for the game version of their Wonderland mission. The novel and manga actually give a reason but not the games so I made one up.