First, collect all eight Sword Orbs. Go to the Ice Country. There should be a small circular island just off the coast. When you land there, Flammie Neko should be there. Then save the game with him. Hold L + R + Start + Select to reset the game. Start a new game at the opening screen and get to the Mantis Ant. You should kill as few Rabites as possible on the way there. Hold L + R + Start + Select to reset the game again. This time, load your old game. The game should resume at the Mantis Ant with your party at your high levels. Hit the Mantis Ant once to kill it. You will receive another Sword Orb. Jema will pull you out and tell you to visit the Water Temple. Call Flammie and upgrade your sword. It will become the Mana Sword, and become the strongest weapon. You will still need to cast the Mana Sword spell for the final enemy. Note: This trick will erase the file that it is used in.