We first must recruit Gau into our party. First enter a random battle here on the Veldt. Defeat any of the enemies in the battle, but do it SLOWLY – don’t execute an attack until the previous ally’s has been completed.
After the battle, Gau will appear. If you hit him, he’ll flee like before (which is why you DON’T rush). When he appears, select the Dried Meat from your "Items" and use it on Gau. After a relatively long and amusing cutscene, Gau will join your party.
Gau arrives naked. That’s not a joke - he has no equipment, so put some on him and cover his shame. Now, he has the ability called Leap . If he uses it on an enemy (whom we’ll call "X") in battle, he’ll leave. He’ll eventually come back after fighting a battle against enemies "Y" and "Z" (just random enemies, okay?). He’ll then get Rages for the Leaped-upon enemy "X" and the enemies in the previous battle ("Y" and "Z").
That being said, there are a ****-load of Rages. So, yeah, get started. Some of them are good, some not so much. Chase him around like that if you want for a while; eventually, you’ll have to go to the Crescent Mountain, found south/southwest of Mobliz.