Fifteen years ago, a powerful Overlord by the name of Zenon appeared in Veldime and cursed its human population. Since then, all its inhabitants have become demons and are to remain that way if the curse was not broken. However, a young man named Adell was the only human unaffected by the curse. Wanting to save his family and return them back to their true form, Adell decides to seek out Overlord Zenon and defeat him. Adell's mother tries to summon Zenon and fails, but instead summons Rozalin, Zenon's daughter. They later go on a quest to find Zenon and return Rozalin to him, and then defeat him so that the curse would be lifted.
The Disgaea series offers a slightly different flavor of strategy RPGs that you can't find anywhere else. The sheer flexibility available is staggering, and anybody interested in this genre should give these Disgaea ports a try, as long as you don't mind the cookie-cutter story and characters.