Protector Cave
After Alex becomes a Dragonmaster, talk to the man behind the counter in Reza at the main building in the north side of the town. He will talk about a cave nearby with a lot of treasure. Exit the town, and you will be able to select that location on the world map. Go there to find a lot of rare items and a hidden Boss. Defeat him to either get the Angel Sword or the Battle Emblem.