Refresh for each blue chest and take appropriate reward:

If Enemy shows up, he takes away:

If Rival shows up, he takes away:

If Both show up, use Rival!

If Prize is 2 items:

Blue Chest: potion, potion, 05 gil, 26 EXP

If Prize is 4 Materia:

Blue Chest: black, purple, white, yellow, 05 gil, 16 EXP

If Prize is 2 AB Letters:

Blue Chest: letter11, letter02, 10 gil, 18 EXP