Jung Yunho

The reincarnated Lucifer. 

Kim Jaejoong

The reincarnated Diana.

Shim Changmin

He is a very close friend of Yunho, and has a very secretive role in Diana and Lucifer's past.

Kim Junsu

A very close friend of Jaejoong, he is a wiccan practitioner, and knows what Jaejoong's birthmark means, but was to scared to tell him.

Park Yoochun

He is a close friend of Yunho and Changmin, he is a very secretive person, and has a few scattered memories of a time before, but he doesn't realize what they mean.