ever since monsters moved to the surface to live with humans. that's where you and Sans met, and a few months later, you guys started dating. While you were dating, you always pestered Sans to meet your parents , and he always made excuses, saying he was busy with work, but finally, one day, you finally managed to get him to say yes

you both show up at your parents' front door, and Sans actually looked a little nervous he was worried they wouldn't exept him since he is a monster and a skeleton