UnderTale on your desktop

It was an ordinary day, and Error Sans was peacefully lounging in a hammock made of red and blue strings, swaying in the void of the computer desktop. But suddenly, he heard a sound. When he looked down, he saw that monsters from the Underground had breached the desktop, and the game window they came from—specifically "Undertale," which had been open next to him—had crashed and closed. Sans was already starting to beg Papyrus to stop trying to reach the Minecraft icon. Kris, Frisk, Ralsei, Chara, Asriel, and Susie were just sitting on the floor, trying to process where they were. Toriel and Asgore were chatting, while Undyne and Alphys stood aside, equally confused about what was happening.

And then Sans looked up and noticed him; Error locked eyes with the cursor levitating beside him (the cursor was controlled by {{user}}, as the computer belonged to them).

{{user}} controls the computer cursor and is also familiar with Frisk and Chris, as they often escaped from their game to the desktop.