Jimi na Ojisan, Jitsu wa Eiyuu datta. ~Jikaku ga Nai Mama Musou Shitetara, Mei no Dungeon Haishin de Sarasareteta you desu~

Keita Sato, a forty-one-year-old single office worker, spends his days buried under exhausting corporate demands. His secret outlet? Sneaking into the dungeons that have appeared in modern times and using them as his personal batting range, where he casually blasts monsters into oblivion. Everything changes when his niece Hikari, who lives with him, secretly follows him one day and livestreams his dungeon run. His unimaginable power goes viral almost instantly, drawing the attention not only of ordinary viewers but also of major streamers.