After a traffic accident, Kazuma Sato’s disappointingly brief life was supposed to be over, but he wakes up to see a beautiful girl before him. She claims to be a goddess, Aqua, and asks if he would like to go to another world and bring only one thing with him. Kazuma decides to bring the goddess herself, and they are transported to a fantasy world filled with adventure, ruled by a demon king. Now Kazuma only wants to live in peace, but Aqua wants to solve many of this world’s problems, and the demon king will only turn a blind eye for so long…
Annoyed that Megumin had still been using his castle for explosion practice, Verdia, after proving easily susceptible to Aqua's purification magic, summons an undead army which is quickly defeated by Megumin's explosion magic.
Wanting to earn some money despite only hard quests being available, Aqua takes on a request to purify a lake filled with alligator monsters, with the others putting her in a cage to keep her safe.
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.
It's great for Kazuma that he brought Aqua along with him, but unlike in a game world, much is missing from his adventurer's lifestyle. No money, no equipment, and even fighting the lowest ranking monsters is a hard-fought battle. That's when they decide to recruit new party members.
A low-grade goddess turned arch priest who works hard to acquire party trick skills, a disappointing arch wizard who can only unleash explosion magic once per day, and Kazuma himself, whose only redeeming quality is his good luck. Kazuma despairs over the completely useless party that's been formed.
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.
With their members being perfectly suited for the job, Kazuma's party, along with Wiz, are chosen to lead an attack against the Destroyer.
Kazuma and the others manage to lure the kite hawks into a cave and deal with them all at once, only to cause more trouble for the other travellers later when Aqua attracts some zombies.
Kazuma and Aqua visit a magic shop run by a kind-hearted lich named Wiz, who reveals herself to be one of the Devil King's generals in charge of protecting a barrier surrounding the Devil King's castle.
As Kazuma notices that Darkness hasn't come back since negotiating with Alderp, Megumin brings in a cat that she names Chomusuke.
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.
Kazuma and his adventure friends Keith and Dust go to a shop run by succubi who provide male adventurers with much needed relief by giving them erotic dreams.
After witnessing Aqua warp the town's citizens with her petty confessional hearings, Kazuma takes a dip in the mixed bath, where he comes across another man who is as sick of the town's behavior as he is.
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. Finding no support from his allies, Kazuma is arrested for treason due to accidentally blowing up a noble's mansion.
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.