Based on the RPG Dragon Quest IV.

In the darkness of a deep cave that humans cannot reach, dwells a devil king ... and you, his lowly goblin servant.
One day while running an errand, you catch news of mysterious hero. And wouldn't it just happen that she's a heroine!
You've got to act fast before Psaro, the evil priests and all the other bad guys find out. Using this news, you assemble a gobliny crew, and set in motion a plan to supplant the devil king ...

[Edited from DLsite English]