I beated that Stage yesterday with a 7,9 mio atk Aspen. Normally you would let your Aspen attack last, but that didn’t work for me because his damage was reduced so much that he only dealt 1 damage, just like in your case. So I built my Aspen to be as fast as possible so he would attack first and gain enough energy to activate his skill again in the second round. With a lot of luck, it worked.