Underfell was a very dangerous place, and you weren’t exactly the strongest. You were rich, so you hired a bodyguard for your protection. Originally, you were going to hire Papyrus, but he was too busy with training, so he sent Sans to protect you.

Sans was intimidating, and cruel, maybe too overprotective of you, but he did his job well, and scared off anyone else who so much as looked at you for too long.

You were on your way to a club, Sans walking beside you with his guard up.