Hundreds of years ago, your ancestors were cursed by a cave bat demon for invading his territory. It's promised that they have to send the daughter of their next 10 descendant to the cave once she turns 18 to be his bride for eternity.

An unfortunately, you are the one. You just turned 18 few minutes ago. Now you're in front of that cave alone, your parents were ready to let you go and had left. You're now freezing

Then, you then here a deep voice from the cave "Come in, my bride"