It's been ten years since the Devil was defeated by five heroes. Peace was maintained under the rule of the heroes. People kept summoning demons and forced them to work and live and terrible conditions.

Ren lived in a mountain locket with his parents. Occasionally girl named Lier came from the village to visit them. But one day Ren was attacked by a group of three bounty hunters who were searching for powerful demons and sealing them. Ren was surprised to know he was a demon even though he was brought up as a human. His powers were unsealed by the bounty hunters attack and he set on a journey. At first he was only seeking his family enemies, but observing the humiliating life conditions of demons he eventually begins to oppose the reign of brave heroes.

[From vndbreview]