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 put 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.

With the addition of a new member, Mitsuba, to the squad, they head to Harajuku to find a vampire settlement and destroy it. When they arrive, they see a girl being chased by the Four Horsemen of John. Knowing it's the vampire's trap, Yu goes to save her.

With the information obtained from the little girl they saved, Yuichiro and his squad goes to the subway station where the vampires are in order to free the people. However, they quickly learn that everything was a trap from the start...

After saving the captured people from vampires, Yu and his unit reach Shinjuku. However, by the time they reach there, the war had already begun and some vampires had gotten through. To prevent Shinjuku from falling, they must fight off the vampires.

Learning that Mitsuba, Kimizuki, and Yoichi are in a pinch, Yu and Shinoa rush to their rescue. Meanwhile, Guren and his troops fight off the vampire's main forces, but Ferid's strength seems to be out of their league, cornering Guren in a tough spot.

Finally, Mika and Yu reunite, but their circumstances does not allow for much time. Mika tries to "save" Yu from the humans, who have been experimenting on him, but Yu wants to save his squad. Torn between Mika and his squad, something in Yu is awakened...

Trying to figure out what happened to Yu, Shinoa tracks down Guren and asks what he’s conspiring to do. However, Guren doesn't answer and keeps it a mystery. When Yu finally wakes up from a seven-day-coma, he explains he doesn't remember what happened.