Leo has defended humanity for three thousand years as the world's strongest hero, but the humans have finally renounced him, and he's quit his job for good. Now free of his past burdens, Leo plans to hand the philosopher's stone over to the Demon Queen as a show of good faith-but little does he know...

Leo has defended humanity for three thousand years as the world's strongest hero, but the humans have finally renounced him, and he's quit his job for good. Now free of his past burdens, Leo plans to hand the philosopher's stone over to the Demon Queen as a show of good faith-but little does he know it will be the cause of a terrible conflict…