I, personally, equipped my axe (Large Crescent if memory serves me) and used the Break Art "Killer Mantis" against Asura. It is a very good BrAr as it sucks out also MP. The damage was not very high (about 30-50). Before that I used spells Herakles and Prostasia to myself, and Leadbones to Asura. It cancels the Surging Blam spell effect. Don't run the risk high, because it's unsafe against Asura's special attacks. Go close to her and use, use and use (BrAr). Very hard and long battle but it can be lasted out.

How do you get the 100% of map?