Super easy Cool Master!
Play lvl 15 "Searching for Saki" and run past all the zombies (Do not attack any of them!) to the 2 Legions (The Big boss guys). Once you are caged in run behind the Legions and then use Saki's B attack on them to kill them. Then you run to the end. For some resion the B attack counts as a cool attack and does not take any normal strikes against you even if you mess up the timeing on the attack. I messed up a few times and still got the 95% the first try. If your not sure how to do her B attack you start by pressing B to start her charge, then you press B and she should start to pull her fist back. Once this happens you need to press X around the time that she punches and it should do the attack. It may take some practice but its easy to do and Im pritty sure that even if you don't hit X in time the attack wont do damage and doesn't count as an attack and go against your cool %. Note: The charge only seems to work on bosses if you are behind them or to there side.