Seth's Backstory

One night, a man was checking out a strange noise he heard when a space squid or something like that crawled in his face and ate his brain. The squid now rests where his brain used to be and is now in control of his body. It gained his knowledge and memories. It learned of mortality and morality. It realized it just ate a dude's brain and given its only point of reference on what to make of that was from a human perspective (as it had no real consciousness beforehand and was merely acting on instinct), it didn't exactly handle it all too well. Wanting to be punished for its crime, it tried telling people what it was and what it just did. They thought "Seth" was just having some sort of breakdown. It was hard convincing people it was not the guy whose body it was controlling on account of it had all his memories, so unfortunately it would be able to pass any imposter tests (like asking a question only the "real" Seth would know). Even the man's fiancee thought "Seth" was merely exhausted and was freaking out over a nightmare or something.

Eventually, the squid's ravings got to the point where they took Seth somewhere to see what was up with him. Turns out there definitely was a squid in his head. (In the world this takes place in, monsters and such are confirmed real, but rare.) So they called some other people to look into it, and after some questioning, they figured this squid-brained man wasn't really a concern at the moment. So they just sent him home and told him to just be quiet about it for now. This frustrated the space squid, but it didn't really know what else to do at this point. And even after finding out that "Seth" didn't really exist anymore, his fiancee didn't seem to want to let go of the body that still looked like him and the memories that only he could've made.

Later it became a teacher at like a monster school or something, and it just occasionally mentions that it is in fact a brain-eating tentacled alien in a meat puppet, and that it doesn't think it's right for something like it to be just roaming around, let alone near kids, whether they be monsters or otherwise, but for some reason it got stuck doing this anyway. Though by this point, its panic and guilt has morphed into a sort of sarcastic exasperation. It may or may not have also developed psychic powers and sometimes spurts ink out of his orifices.