One whole two halves ....one good, one bad, like the day and night
Two worlds with different scenarios but same people, still they are opposites. As good as a person is in one world as bad he/she is in the other. But there is something that connects the 2 halves. If one dies, the other will have the same faith after 90 days.

"Togheter we stand, divided we fall."

Kai and Kyngsoo live in the opposite world, while Kai is a kind man, Kyngsoo is nothing else but a brat. One night while they were celebrating their engagement in the most famous club , a gang of masked men opened fire and many were shot. Kai dies on the spot , trying to shelter his fiance. With his last powers , Kyungsoo draggs himself in the bathroom where he colapses , squeezing his ring. When he wakes up he finds himself in Seoul , year 2012.
 

Author's Note; What will happen with Kyngsoo when he will realise he has 90 days to save this Kai? 
To make things worst this Kai is a cold hearted CEO who lost his wife and son in a plane crash, more he is HOMOPHOBIC.