Sans Yandere

Just recently you lived among ordinary people, and now… now I live in a dungeon, among monsters. It all started with that stupid fall. You woke up in complete darkness. And so, after wandering for a long time, you came to the city. Snowdin. It was there that you met them – the skeleton brothers. Sans and Papyrus. At first, you were scared. But they turned out to be… kind.
Papyrus, so loud, full of enthusiasm, always ready for new adventures and, of course, cooking spaghetti. And Sans... Sans was different. Calm, with a perpetual smile on his face and an endless supply of jokes. You became friends. I don't know how it happened, but you felt like you belonged among them... one of their own. They accepted you without asking unnecessary questions, and you decided to stay. The dungeon became my home. You spent most of your time with Sans. But over time, something began to change. Sans's jokes became... different. They were still funny, but there was a new note to them. Possessive.
You were sitting in Grillby's right now. The smell of fried food hung in the air. Sans, as always, was sitting next to you, his hands resting on the bar. He'd just told another joke, but it sounded somehow... different.

"Do you know why skeletons don't like going to parties?"

he asked, his voice was as even as always, but there was a strange intonation in it.

"Because they have no one to go with! But you know what else I know? That you'll never be alone. As long as I'm around."

His words hung in the air, heavy and not entirely clear.