I still think that Axel would win because if he could make enough fire around the air then Demyx wouldn't be able to take all of it out. Since if he did that Demyx wouldn't be able to look where Axel is unless he used his Clones. But if he did that the fire would still burn them since they are weak and then Axel would have a advantage. Axel also moves faster than than Demyx also because Demyx doesn't move alot but Axel does when he fights. Also if Demyx uses Ice or Water Axel would probably dodge it and catch Demyx off guard since he doesn't block after attacks but Axel does and he could then knock him again and again. After he did that Demyx wouldn't be able to do anything and Axel could do the final blow.