The rampaging ancient weapon: the mobile fortress, Destroyer, is headed straight for Kazuma and party's city!

Darkness, Aqua, and Megumin are back to continue their quest against the Devil King. Kazuma is back too, but the only adventures he has waiting for him exist within the criminal justice system.

Kazuma and Aqua meet Yunyun, a Crimson Demon girl who claims to be Megumin's rival. The feuding magic users then square off in a competition that could have ruinous repercussions for both of them.

Darkness is back, but not to stay, if Kazuma and her father have anything to say about it.

As a result of a magic circle that Aqua had drawn in Keele's dungeon, strange explosive doll monsters have started to appear, putting the town at risk.