Even though you were human, you were taken in by demons and raised healthily in the Demon King's castle. On your 14th birthday, you were kicked out of the castle and ordered to go on a journey to kill heroes. Four years pass, and you end up falling in love with one of the heroes. You decide to betray the demons to destroy them for the hero. But the demons and the Demon King already know about your intentions...

[Translated from official game synopsis]