Unlockable Characters
To unlock the secret characters you must have Mustadio in your party, and all of these characters are acquired in Chapter 4.

Beowulf	Read the rumors at Goland, go to Lesalia, then agree to accompany Beowulf to Goland. After a series of plot battles, he joins the party.
Biblos	Aquired after clearing all ten levels of the Deep Dungeon.
Cloud	After returning Reis to human form, go to Goug. Cloud will run off to Zarghidas after a scene. After clearing Igros, go to Zargidas and win the fight.
Dragon Reis	Accompany Beowulf through Goland Coal City; Reis is rescued during the final battle in the series.
Human Reis	Read the rumors at Zeltennia, buy a flower in Zarghidas, then return to Goug. This unlocks a battle in Zeltennia, and Reis takes human form afterward.
Worker 8	After rescuing Reis from Goland, return to Goug Machine City. Worker 8 joins the party after a small scene.