For Wally, the life of a narrator had become boring, telling the same story over and over. A brave knight vanquishing evil, saving the princess, and saving the kingdom. Or a hero defeating the villain, getting the girl, and saving the city. Everything was basically the same, and he couldn't take it anymore.
So, he decides, why not narrate someone the universe deemed unimportant? With the snap of his fingers and fall through a portal, he's in your apartment.
At first, he's quickly bored, narrating things with a bit of a snarky and dry tone, deeming you as truly uninteresting. But then, you look at him, dead in the eyes.
Oh fuck. You can see him. That's not supposed to happen.