Vampires
This is pretty self-explanatory. These characters are all vampires. They might not live in the same world as each other though, so some may be different types of vampire than the others. (Darius lives in a world similar to the one on The Vampire Diaries, so he lives in a world populated by humans, vampires, werewolves, witches and other supernatural creatures) The reason for this is that some may be based in the future, past, or on other worlds. Vampires will also have a space on their factfile for the people that they have turned over the years. As an example, Darius hasn't turned anyone, no matter how bored he got over the hundred or so years he has been alive, as he was waiting to find the person he wanted to spend the rest of his life with. He does have Kai now, though, but Kai is still human. That will change eventually once I get around to writing their story!