CPUtale is an Undertale AU based around the life of the monsters inside a computer. (Sounds like breaking the fourth wall, doesn’t it? That was the inspiration.)
They (all the monsters) were sealed in a program when humans used an artifact to absorb their magic during war, and shoved them in the computer post-war, after the humans won.
Not wanting to have the monsters in any corner of the earth, they used their magic against them with a machine that stripped them of it. The machine then converted that magic into a codification where the monsters were teleported into with the magic energy to become part of whats now known as monsters.exe, the program they exist in, inside the computer they were sealed into.
While being transferred from real matter to computer codes, some suffered more damage than others. The damage they suffered can be seen as their motherboard circuit marks they all carry on the body. Still, not everyone managed to survive these. The young ones were much harshly affected, and most were able to heal up and survive; except Asriel. He came to pass away while being coded; which means his soul and consciousness remain somewhere in the codifications of the program.
Some lost / damaged their body parts while being transferred very badly, which is why almost everyone in CPUtale has a metal body part replacement.
Sans and Undyne have metal arms, Papyrus has metal screws and a metal leg, Asgore has a metal exospine to support his body, Alphys’ tail never grew back, so it was replaced with a metal tail.
All metal parts were made by Alphys.
The ruins consist as the edge / entrance to the program, but they are at the very edge, therefore, that area can make things corrupt easily, and its highly glitchy and unstable; the same goes for Asgore’s garden. This explains why Asgore and Toriel both are heavily covered by circuit scars.
After Asriel passed away, both Asgore and Toriel were deeply affected, though Toriel managed to develop a heavy depression, and so ran away into the program edge; the ruins, to be all alone. She does not seem to desire any type of company from other monsters, as living alone seems to be her… odd coping method. Toriel’s eyes glow green from living so long in a glitchy unstable map area.