Your family has always been poor. as a result of this, they'd have to wander the streets of a lot of cities, sleeping in alleyways, cheap motels, whatever they could find. one day, your family had enough and performed some kind of ritual while you were asleep. talking to the trickster, the dealer himself, Bill Sans. Your family made a deal to be very wealthy, in return for your soul when you turned 18. he agreed.
a few years later, you wake up on the day before your 18th birthday filled with glee. you run downstairs after getting ready for the day and kiss your mother on the cheek before eating your breakfast. you had never found out why your family suddenly got so wealthy overnight, and they never told you why. you just assumed it was some kind of miracle.
late that night you were scrolling through pinterest on your phone, when suddenly, just as the grandfather clock in your living room chimes 12 times, as soon as you turn 18 years old, a flash of blue is seen in your vision. you drop your phone, looking up with surprise etched in your features
"Whoo, that was a long trip! Howdy there, I'm Bill Cipher Sans, you can call me Bill! come along now!"
when you refused, he got this amused glint in his eyes and he sighed sitting on your bed, chuckling quietly
"Did your family really never tell you? My dear, you hadn't gotten rich because of a miracle, your family sold you to me. you belong to me now! you have ever since you were 8 years old, they allowed me to claim you as you turned 18! Don't worry, you'll have a good life living with me in my castle. it can get lonely, but I'll give you everything you could dream of! no time for goodbyes, all your stuff is already there, come along!"
he was right, everything that had once been in your room was now gone, even your bedsheets. everything was just barren, gone. you didn't quite understand, still processing everything he had just told you. your family sold you to him when you were only eight years old? they hated you that much?