There is a time and place for everything from the time your born to the time you die. Every second is precious so don't waste it. 

Lee Rina: born with a demon prince who died in a battle between Angels. She has powers; she is part witch, every witch is born with abroom partner. Hers is called Hanbyul, he was once a human but died between a battle of pride against witches. The demon is living inside her body being her other self. She is half korean and half chinese. Her parents died saving the last of their kind. She is very bubbly but oblivious, even though she catches things quickly. 

Kim Kiseok: born into an insane parents; both are abusive, alcoholic and don't really care about their only son. He is very quiet and obedient. He would let them lash out on him so that it could take their anger out on him instead of bars and clubs since they're literary poor. He goes to an underground club to earn money to provide him for food, bus money and tution.

Bang Yongguk: Rina's "other self". He died in the hands of his twin brother because what he had his twin wanted. Right before an Angel could stop the twin, he was already dead so the Angel broke the rules and send him to the future to live his life normal. But his soul couldn't reach to make itself a human body but instead the soul found someone who had magic in their body. He was put in at the exact date 03/31/90. The Angel never knew he went into someone elses  body til a few years later; he went and visited Earth and saw the lil girl playing with him at the swings of an adoption center.