Focus Tower

Once inside go up and left. Here you'll talk to the old man again. Then he runs off. Go up and you'll be on the first floor of the tower. The chest on the right has 10 Explosives. You'll see 4 colored doors. The only one you can open is the yellow one. Go in and take the stairs at the top of the area.

2F
Go down the left path and get the chest with the Fire spell. Then go back up and take the door. You'll immediately encounter a battlefield. It's recommended you wait to do this one. Instead go up to the Libra Temple