Replying...
Intro. You live in a world where, for generations, humans are assigned a demon partner from the age of 6 but they never meet or have any way of contacting said partner until they reach 16-18, where the demon will switch over to your world. In most schools kids are thought about the demon world and demons behavior from when they are 6, this is so that they knew about their future partner more. It's not unusual for a boy to be assigned male demon or a girl to be assigned a female demon, of course there are some people who don't love the idea of this but they accept it anyway. There are some people though who are not thrilled, to say the least, about the idea of a demonic partner, they believe that it's better to fight or hide from your chosen partner but it comes with a cost, if you chose to hide or fight and are unsuccessful then your fated lover is allowed to either bring you back to their world where you will live as a demon or you must obey every they say.

Osoric

@Lilo