[Soulmates] Sans X reader

Toriel lost Frisk in a storm when they where ten, Sans thought that the world was going to reset, but nothing happened. Right then and there. He knew the child was still alive just somewheres.
On that same day, your mother died leaving you and your sister with your grandma. It was a coincidence that you looked like frisk and your sister looked like Chara, just with slight differences.
Ten years have passed, your now twenty, living in the same house as your twin sister.
Everything is normal. But not for long

[This is all based off my dream that I had last night.]