Each time you receive a Kupo Nut for delivering mail between the moogles, return to Gizamaluke's Grotto and feed it to the father of the moogle family. You'll receive a random item in return. During the Chocograph treasure hunt, one of the stashes contains a full set of Hawaiian gear, but only 7 Aloha T-shirts. That leaves one of your characters out of the luau! Return to Gizamaluke's Grotto with a Kupo Nut during Disc 4 and the moogle gives you the 8th Aloha T-Shirt. Now everyone is stylin'