Vampires have taken over the earth in a series of past wars, and now keep humans alive only for their entertainment and nourishment. Key is the overseer for a "concentration camp" for humans, meaning she works with the vampires and rarely has her blood drank. Years before, when the vampire wars were just beginning, she meets Tetsuo, a vampire who she quickly falls in love with. She travels with him throughout the war and is protected. She wants him to feed off of her, but he refuses. After the wars are over she moves to the camp, Grade Orange, and works with another vampire, Mr. Charles, to keep the other humans in line. She tries to forget about Tetsuo, who she realizes never loved her. After a human at the camp dies by suicide, Key starts to have doubts about her cooperation with the vampires. She is sent to another camp -- Tetsuo's camp -- after another human there also dies. Tetsuo tells her he will reward her by finally turning her into a vampire. She means to refuse this after she reflects on what the vampires are doing to the humans. Even at Tetsuo's camp, a Grade Gold facility, where the humans are treated well, they're made to have sex with each other before they are fed on. It's wrong, she thinks. The girl who died at Tetsuo's facility is Penelope, who looks like a young Key. She realizes that Tetsuo was planning on turning Penelope into a vampire, but then she died, so he chose Key. She means to refuse his offer but he turns her anyway, and she feeds off the other humans in the camp.