Rimuru is building a dungeon in preparation for the upcoming festival. It will feature treasure chests containing weapons made by Kurobe, and Veldora will inhabit the deepest floor as the final boss. Then Milim suddenly shows up with a suggestion...
She's going to build 
a labyrinth under the arena.
سوف تبني متاهةً تحت الحلبة
Va a construir
un laberinto debajo del coliseo.
Va a construir
un laberinto debajo del coliseo.
E a me è venuta l'idea di farle creare
un labirinto sotto l'arena!
Ela vai construir um
labirinto sob a arena.
Она сейчас под ареной
потихоньку строит свой лабиринт.