| Synopsis |
Prologue[]
After Kazuma repeatedly beats Aqua at card game thanks to his gaming skills, he tells his cheat item to go find some job for him. As he and Megumin debate over quests against Giant Toads and other jobs, Darkness bursts in with a notice saying the Nightless City, which is a dungeon that requires paying a fee to challenge, has recently been ranked as "impregnable". Her three companions, however, try to ignore her suggestions to challenge it by talking about jobs to subjugate lake monsters, bet money and fried Neroids, until she states that clearing this dungeon which hasn't killed anyone will grant a huge reward and widespread fame. While Aqua and Megumin agree to go, the skeptical Kazuma manages to get Darkness into confessing that she wants to go because the dungeon, which only allows entry for mixed gender parties, is known for sexually harassing female adventurers. With his party members all pumping to go, Kazuma has no choice but to follow on this journey that he has bad feelings about.
Chapter 1[]
The party trudges to the dungeon situated not far from Axel, when they spy dust clouds kicked up by livestock infested by the parasitic Cowdyceps. Aqua confidently charges out to meet the herd thinking to make roast meat out of them, only to run back when she sees how disgusting the pulsing face-like cysts growing on the infested goats are. Dragging the fantasizing Darkness with him, Kazuma and the others hurriedly make their escape.
Chapter 2[]
Arriving at the Nightless City which has a huge welcoming sign at the closed entrance, the party learns that it only allows mixed gender pairs in to challenge, which is begun by the challengers writing their names on a pad before depositing the fee into a box. As a panicky Aqua and Megumin wants to let only Kazuma and Darkness to go, Kazuma blows open the entrance with a vial of Wiz's potions so all four of them can enter, prompting the girls to comment on his despicableness.
Advancing in the pitch black dungeon without turning on lights and trying to keep quiet so that they won't attract monsters, Aqua plays a prank on Megumin by groping her, so Kazuma does the same on Darkness only to enrage the crusader for being too soft handed. Yet when Darkness squeezes Kazuma for it, he detects monsters approaching and Lurks into hiding, and nearly gets a haircut after the annoyed Aqua directs Darkness into attacking the area where he is at. Megumin then finds herself entangled by a breed of Green Slime that only melts clothing, and to her horror Kazuma proposes turning on the lights while Darkness wants to capture the Slime alive by taking her outside, though the two of them get sorely disappointed when Aqua purifies the Slime into water.
Proceeding ahead, they reach a glowing sign warning them to beware of ghosts, before Aqua is frightened out of her wits by a ghost model. Persuading Aqua to take the lead again so she can sweep traps for them, the party progresses into the hazardless dungeon that seems more like an amusement park's haunted house. Although Aqua keeps getting scared by various childish traps, the others continue to praise her as a goddess for her to lead on.
The party approaches a sturdy door that Aqua thoughtlessly pulls open, but upon entering the room beyond where Kazuma doesn't detect enemies, the girls feel something really unpleasant present. Kazuma accordingly lights a torch with Tinder, revealing the presence to be cockroaches that the girls call "kings of terror". After stepping on one of them, Kazuma hears from the girls how the cockroaches will bring terror to their household by laying eggs in their mansion at night so the four of them will get crawled all over, prompting him to frantically kill every single one of the pests, following which the girls comfort his traumatised soul.
Later drawn by some lights, the party witnesses glowing fairies flying around in a romantic scene, though the mood is broken when Aqua and Megumin goes and captures the precious critters.
Chapter 3[]
Having walked a long way, the party sees another sturdy door that the heedless Aqua rushes to open, but inside the misty room where they expect to see the boss, the four of them instead see a fake Kazuma. When Megumin theorises that it is a Doppelganger, the fake Kazuma attacks, only to be easily stomped by the overjoyed girls as they take out their daily frustrations on the identically weak copy of Kazuma. However, the downed fake Kazuma proceeds to Steal the girls' underwear as well as use various magic to confound them, forcing the girls into begging the real Kazuma for help.
The real Kazuma accordingly conducts a ferocious battle of childish swings with his copy, until the fake Kazuma tempts him with the underwear it had just Stolen. With the real Kazuma refusing to be tempted due to the looks his companions are giving him, the fake Kazuma proceeds to use Steal, only to be distracted when the real Kazuma beats it to Stealing nearly all the clothing from Darkness, allowing the real Kazuma to cut it down.
While Aqua later tries to stop Darkness and Megumin from immediately killing Kazuma, the fake Kazuma tells using a different tone that the party has passed the trial, with the real Kazuma explaining that the whole thing is a game for bonding adventurers together. As the girls express their hopes of clearing the dungeon, the fake Kazuma announces that the real Kazuma is qualified to take the final trial, which he readily agrees to perform alone.
Epilogue[]
The girls comment about their tour as the party later leaves the dungeon, while Kazuma tries to hide the fact that the final trial was a selection to clear the dungeon and make it disappear before receive huge rewards, or retire from the tour and leave the dungeon as is, so that the dungeon he and other male adventurers had left intact will continue to let them bond with the girls they enter alongside. Kazuma then attempts to invite Darkness into challenging the dungeon again with just the two of them, before Megumin Explodes the dungeon of sexual harassment. While Aqua is upset over the glowing fairies she had captured being destroyed by daylight, Kazuma laments not having chosen to take the reward.