Kojo Akatsuki used to be an ordinary high school boy—but that was before he became the Fourth Progenitor, the most powerful vampire of all time. Worse—he doesn't even remember how it happened. Middle schooler Yukina Himeragi, meanwhile, is the attack mage sent to observe him—and to stop him if he gets out of control. But was it really a good idea to send a cute girl to observe a massively powerful vampire boy whose abilities activate whenever he gets aroused? And on an artificial island populated with all manner of demonic individuals, each with their own designs on the Fourth Primogenitor—!

Nagisa has collapsed! Kojou rushes to the hospital, but suddenly a mysterious girl appears, and she looks just like Avrora, the former Fourth Primogenitor. She backs Kojou into a corner—but is she the real Avrora? Through this encounter, Kojou regains his lost memories, what will he remember? Finally, Kojou's past and the secrets of the Fourth Primogenitor are revealed!

When Kojou Akatsuki went to visit his sister in the hospital in middle school, he met a vampire named Avrora. Once he learned she was the key to saving Nagisa's life, he helped Avrora escape. Now, the weapons dealer Zacharias is telling him to hand over Avrora in order to rouse the fourth primogenitor! As Zacharias' plans plunge Itogami Island into peril, the fourth primogenitor finally awakens...

Blue Elysium is a newly constructed, additional manmade isle off the Demon Sanctuary of Itogami the latest, greatest resort, boasting pools, and an amusement park! Yaze schemes to invite Kojou and the others to the isle before its public opening, but somehow the "free" trip lands Kojou in a horrid part-time job. Meanwhile, Sayaka Kirasaka, Shamanic War Dancer of the Lion King Agency, visits Blue Elysium as well. Her to rescue the mysterious girl Yume, held captive inside a research facility. But, an unknown Attack Mage appears before Sayaka, a "Priestess of the Six Blades" using the same techniques as Yukina!

A civil war suddenly erupts in the Chaos Zone, the Central American empire ruled by the Third Primogenitor. Kojou & Co. sense that someone is backing anti-government forces from the shadows. Suddenly, a mysterious suitcase arrives at Kojou's apartment from the Chaos Zone - and the sender is Dimitrie Vatler. Inside the suitcase sleeps a mysterious foreign girl named Celesta. Kojou and Yukina look after Celesta while she, regarding Vatler as her savior, disparages the two of them with a poisoned tongue. However, Celesta, the "Bride" of Zazalamagiu, harbors a frightening secret unknown even to her-!The long-awaited tenth volume of the school action fantasy series about the World's Mightiest Vampire and the man-made island of never-ending summer!

A New Year on Itogami Island is right around the corner, and for Kojou and Yukina, that means cutting off their contacts and returning to the mainland for a top-secret rescue mission. Coincidentally, this also means zero contact between Yukina and the Lion King organization. Can the fearful duo see their mission through to the end, or will they be overwhelmed by an unexpected enemy?