You—the hero who struck down the Demon King—is framed for the king's assassination on the night of celebration, and becomes a prisoner awaiting execution.

On the eve of the execution, the voice of the girl Rei from the next cell shoots through his sealed fate. The forbidden power of the summoning gun loads victory and loss into the very same bullet.

Once praised as a hero, he walks the world anew as a sinner. A journey begins—chasing the lost truth, and the time carved into every bullet.