Banished from his birthplace when he was only six years old, Claes promised a future to Hinoka, a girl he met on his way to his birthplace, and they made a living as adventurers. However, he is nearly killed by the wiles of a fellow party member, the hero Rondo, and even Hinoka is taken away from him. In desperation, Claes activates the gift "Holy Grail" and realizes its true use and vows to take revenge on all, but its power is an out-of-the-box ability that fundamentally overturns the world order and drives people mad. The humans, enslaved by the gift, and the demons, who want to take advantage of it, begin to invade with mad science. Crais is caught up in the madness of the three-way battle.