The OC is know to be the only princess left in the moon kingdom, she lived a peaceful life but then the other humans ( like herself ) decided to attack the Exo kingdom.

it backfired 

her peaceful life was razed , her father signed a peace alliance bethroning her to the Exo kingdom’s oldest son Byun Baekhyun

the Exo kingdom is feared by normal people , they loathed them 

why you ask ? 

Because there lived...monsters       link : https://www.asianfanfics.com/story/view/1140828/monster-comedy-romance-supernatural-exo-baekhyun-royalau