In this world monsters and creatures of myth are real and when they were reveled to the world by a certain event, the world governments united to eliminate this threat and at the end of this brutal conflict most creatures were killed, the others were enslaved or studied. The enslaved had only one job and that is to kill the ones left in the world, the old gods.
At the current time the few gods left are on isolated islands. The world government sent ships to the locations and each of them has a team of 5 mythics to kill the gods on the islands. On one of those ships in addition to the mythics, there is a boy drafted into this military operation by his grandfather named Hashi.