Manga by author Imano Yuki

Sato Keita (41 years old, single), a corporate slave salaryman who spends his days doing tedious work while feeling stressed, relieves his stress by sneaking into a "dungeon" that has appeared in the modern world and smashing through violent monsters as if it were a batting center! One day, his niece Hikari, who lives with him, secretly follows him and broadcasts the whole thing...!! ?