Hideo Abe, a 40-year-old employee at a black company, works tirelessly every day. Living alone, he often despairs over how his life seems to be just trudging along without change. One day, while feeling particularly down, he discovers an animal abandoned in a cardboard box. Yearning for some comfort in his life, he looks inside and finds a small slime.

In a world where dungeons have appeared in modern times and monsters can be tamed, our protagonist's life takes an unexpected turn. By taming the slime, he inadvertently embarks on a side job as an adventurer. This leads to changes in his daily life and relationships, and he begins to experience a heartwarming, slow life with his slime companion.