Stuck in the grind of stressful, tedious work, 41-year-old bachelor and salaryman Keita Sato's only escape is an unconventional stress relief method: venturing alone into newly-formed "Dungeons" in the modern world and treating the vicious monsters inside like baseballs at a batting center, smashing them away with gusto! But one day, his niece Hikari secretly follows him, and—much to his surprise—she livestreams his monster-bashing escapades for the world to see...!?