Tsuujou Kougeki ga Zentai Kougeki de Ni-kai Kougeki no Okaasan wa Suki Desu ka? S01E01 - The Boy Thought He Was Embarking on a Great Adventure… But, Uh, What's Going on Here?

Teenage boy Masato Oosuki was chosen to beta test a new MMORPG, where you're actually teleported inside the world of the game. But once he gets there, he finds his mother has followed him, and she's incredibly strong, too.