A deadly virus sweeps the earth, leaving behind only children and vampires. Yuichiro Hyakuya and the other orphans are captured by these vampires and are forced to provide them blood in order to survive. Fed up, they plan on an escape, but...

After his escape from the vampires, Yuichiro learns that humankind hasn't perished. Determined to get his revenge, he joins the Japanese Imperial Demon Army. Four years later, Yuichiro feels his training is enough, but his bad attitude gets him suspended.

A student sneaks into the Forbidden Chamber, where the army keeps a demon for training. To show how dangerous a demon is, Shinoa takes Yuichiro and Yoichi there, but her plan fails when Yuichiro ignores Shinoa and starts to fight the demon.

Mikaela, who was thought to be dead, was actually turned into a vampire by Krul and is working with them. Meanwhile, Yuichiro starts his first day at the Extermination Unit's training school, but soon gets into a fight with one of his classmates…

Eager to obtain the Cursed Gear, Yuichiro tracks down Guren and persuades him to provide him a chance at the Contract Ceremony. Passing Guren's test, Yuichiro, Kimizuki, and Yoichi puts their lives on the line to make a contract with the demon kings.

Yuichiro, Kimizuki, and Yoichi begin their Contract Ceremony to obtain their own Cursed Gear. The demons attempt to take over their bodies, and while Kimizuki and Yuichiro manage to subjugate them, Yoichi fails the trial and becomes a human-eating demon.