If you transfer your data from the Golden Sun, you probably will have the Force Orb to use The psynergy move, Force. You can use Force to knock down the log to the left of the blacksmith house in Yallam. Hop across the log then use Cyclone to reveal a secret underground entrance. Go into the cave and follow it all the way through. When you are outside, you will find a chest which contains the blade, Masamune. It unleashes Rising Dragon, that can do up to double the damage if two Dragon Spirits hit an enemy.