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 is surprised to discover that Vanir had an extra life and has since quit his position as a commander to work at Wiz's shop, striking up a business partnership to sell products from Kazuma's world.

Vanir gives Kazuma the choice of either selling the intellectual rights for his real world products for a one-off payment of 300 million eris, or maintaining a profit-sharing contract of 1 million eris a month.

The party makes their way to Arcanretia, a city known for it's recuperative hot springs! But what they don't know about the city might spell doom for their vacation.

Evading the angry mob, the gang discover that the source of the town's water is being poisoned by the man from earlier, who is revealed to be one of the Devil King's army leaders, Hans the Deadly Poison Slime.