Suddenly appearing in the modern world, "otherworldly dungeons" have taken center stage as the ultimate entertainment, with dazzling live-streamers broadcasting their dungeon-conquering adventures to massive audiences. The craze has reached unprecedented heights. Meanwhile, Eita Yamaoka is stuck in the drudgery of a soul-crushing corporate job, living a life far removed from this flashy phenomenon. His sole source of joy? Playing with his pet-like dungeon monster, a simple slime. But unbeknownst to the world, the floor where Eita and his slime casually frolic is one that even the top-tier streamers struggle to reach—a humanity's yet-unconquered dungeon level!