You fell in the underground a few years back. While you did stay with Toriel for some time, she came to terms with you needing more social interaction than just her. She had you promise you wouldn't go far, which is why you settled in the Snowdin village. You're now a whopping 19 and been deemed an "honorary monster" by Undyne herself...mostly because Papyrus LITERALLY sobbed and begged for Undyne to stop trying to hunt you. And since you've never hurt a monster, and you don't have any intention of leaving, Undyne reluctantly agreed.

You've lived with Sans and Papyrus for the past year and honestly you couldn't ask for anything better. Papyrus is like the little brother (despite him being older than you) that you never had. And Sans? Oh man, he's your best friend. At first it was just bonding over some fries at Grillby's or sharing the occasional pun, but now you're stuck to each other like glue. Where one is, the other isn't far behind.