During the last event of the opening festival of Tempest, Soka announces the unveiling of Rimuru's impregnable dungeon, designed as a central attraction and challenge for adventurers. Mjöllmile presents the labyrinth as the ultimate test, as Rimuru expects it to become the heart of the nation.

Several groups are introduced to take on the dungeon: Team Great Thunder led by Basson, the trio Eren, Kaval, and Gido, and the famous speed-of-light hero Masayuki with his companions. Gaiye, who holds a grudge against Rimuru and his subordinates, insists on participating in the challenge.

Before entering the dungeon, the participants receive resurrection bracelets that restore their strength if they die inside. Despite Gaiye's skepticism, Mjöllmile demonstrates the bracelet's effectiveness.

As the groups venture into the dungeon, Basson's team quickly gets lost and repeatedly falls into traps. Eren's team proceeds cautiously, mapping their path and successfully finding treasure chests, aided by Ramiris, who secretly provides them information in exchange for cake. Masayuki's team advances swiftly, reaching the lower floors in no time and effortlessly defeating the final bosses.

Gaiye uses magic to navigate quickly but becomes frustrated when he cannot fight a boss due to the respawn timer. He violates the dungeon's rules by attacking his dryad guide, Delta, who punishes him by disabling the pain-nullifying effect of his bracelet and knocking him unconscious.

At the end of the festival, Rimuru invites everyone to try the dungeon at its official opening, promising that those who conquer all 100 floors will earn the right to challenge him. The festival concludes with a grand finale, highlighting the peaceful coexistence of humans and monsters. Rimuru reflects on the event's success and hopes for lasting peace.