Isekai Ojisan

Seventeen years ago, Takafumi's uncle fell into a coma, but now he's back like a man risen from his grave. Soon, Takafumi discovers two bizarre things: His uncle treasures video games above all else, and, while comatose, he was actually transported to another world as some heroic guardian! Now, not only does Takafumi have to room with an uncle who is literally magical, he also has to catch the guy up on two decades of history—smartphones, high-speed internet, modern anime tropes...and the traumatic outcome of the '90s console war!

(Source: Yen Press)