Kaisoo are divorced but are obliged to pretend they’re still together for their son’s wedding because the latter's in-laws are devoted Christians and think that marriage is the biggest sin, so Kyungsoo and Jongin have to pretend to be in love. 

Inspired from the movie "The Big Wedding". 

I still haven't decided if I want this to be a oneshot or a chaptered fic,I need opinions sigh.