All of the weak monsters have gone into hiding since a leader of the devil king's army has settled in near town. Kazuma, who had been focusing on improving his skills, is stuck at a standstill. With nothing else to do, Kazuma tags along with Megumin's training, which consists of unleashing explosion magic into an abandoned castle.

Dullahan, a top leader in the Devil King's army, yet again appears at the city in a frenzied rage.

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

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.

After returning from his trip to Arcanretia, Kazuma is living life without a care in the world, thanks to his debts being all paid off by the reward money he earned from eliminating one of the Devil King's generals, Hans. One day, a rookie adventurer named Ran comes up to him in the Guild Hall asking for a handshake. She's apparently become a fan of Kazuma after his consecutive defeat of the Devil King's generals! This puts him in an amazing mood, but it's not long before the Guild receptionist Luna appears, asking him to take on a quest to eliminate a golem. Wanting to look good in front of a fan, Kazuma ends up accepting, and heads towards ancient ruins with Aqua, Megumin, and Darkness in tow.

Kazuma and the gang fail to defeat the hydra in the lake near Axel. The gang hopes to rely on knights from the capital, but they've been delayed due to a bandit disturbance for which a bounty has been issued. Darkness, however, is obsessed with the hydra.