Moto Tansakusha no Ojii-chan: Mago ni Segamarete Dungeon Haishin o Hajimeta njaga, Nanjaku na Wakazou o Shikaritsuketara Bazuriotta wai

"This is how you kill slimes!"
Summer vacation. The blissful time when his beloved granddaughter, Mana, comes to visit.

“Hey, Grandpa, stream a dungeon run! You used to be an explorer, right?”

He doesn’t really get it, but he can’t refuse when his granddaughter begs him. Though it’s been thirty years, former explorer Genji Kudou dives into a dungeon once more. Genji’s way of conquering dungeons is completely different from modern common sense. He ends up lecturing an obnoxious streamer he happens to run into. Various things pile up, and before long, he goes viral all around the world. Today as well, Genji drives his beloved mini truck toward the dungeon.

(Source: Mag Garden, translated)