After you go through reviving all four of the different elemental spirits, there are wondrous battles to be fought around Krage. However, a lot of the enemies you will meet there tend to run away from you. Use the EvilSlash skill on them. It hits relatively enough times that you will kill more of the MetalKings than will run away. As long as you have all of your party equipped with this skill, you will get that many more chances of having it succeed. It does not matter what level you are at when you reach this stage of the game. The hits with EvilSlash are all critical, and will kill the MetalKing if you hit it for 33,000 experience each.