Any sort of relationship between a demon and an angel was forbidden. An angel that has contact with a demon is to be banished from Heaven, cast to Earth to live as another entity, unseen and alone. A demon that has contact with an angel suffers the same fate, living between worlds with no one to accompany them. The humans are always unaware, blind to the demons and angels that are very much real.

Leo

Leo is an angel who doesn't have much interest in Heaven. He finds it boring because all the other angels are too well-behaved to do anything interesting or exciting. Leo always wonders how he made it to Heaven when he wasn't the best as a human. He constantly makes trips to Earth to watch the humans go about their daily lives.

Ken

Ken is a demon that gets easily bored of the screams of the suffering souls, and he doesn't find much fun in torturing them alongside the other demons. He's surprisingly soft-hearted for a demon, and he was a good person as a human. He enjoys going up to Earth to cause a little trouble, but not enough to injure anyone.

Taekwoon

Taekwoon is a normal human boy with a normal human life. He isn't aware of the existence of demons and angels. Taekwoon lives with his roommate Jaehwan in an apartment in Seoul.

Jaehwan

Jaehwan is a normal human boy with a normal human life. He isn't aware of the existence of demons and angels. He lives with his roommate Taekwoon in an apartment in Seoul.