Strike the blood / Mikumo, Gakuto

Nagisa is away on a trip to the mainland, visiting her grandma, and has not been returning her friends' calls or texts. Yukina, then, more worrisomely, loses all contact with the Lion King Agency, and when she and Kojou attempt to find answers they discover evidence of a magical incident, prompting Kojou to risk all and go to the mainland to find Nagisa.

Chaos erupts on Itogami Island as key personnel from the Gigafloat Management Corporation wind up assassinated, one after another. The culprit is the self-proclaimed Demon Sanctuary destruction group called Taartarus Lapse. Meanwhile, the soul of Avrora has been bleeding into Nagisa's consciousness, even as the mysterious girl "December" appears, who is the secret leader of Tartarus Lapse.

At the sealing ceremony for the relic of The Cleansing, the former Fourth Primogenitor who was sealed within Nagisa awakens, surging with magical energy and causing the calamitous being at the bottom of Lake Kannawa to wake up and threaten the world.

The tentative peace between Kojo Akatsuki, the Fourth Primogenitor, and Yukina Himeragi, the girl sent to observe him, ends with the appearance of Dimitrie Vatler, an emissary of the Lost Warlord.

"Koju Akatsuki used to be an ordinary high school boy--but that was before he became the Fourth Primogenitor, 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 artifical island populated with all manner of demonic individuals each with their own designs on the Fourth Primogenitor--?"--Back cover.

"Aya Tokoyogi and six other hardened magical criminals have broken out from imprisonment. Their goal--to completely erase the Witch of the Void, Netsuke Minamaya, from existence. But they might not even need to try very hard now that Natsuki has lost all of her powers and memories, reverting to a child who depends on Asagi for everything. Meanwhile, as Yukina and Kojou search for a way to save the horrifically wounded Yuuma, help comes from an unexpected place--or rather, person. How these events will unfold in the Demon Sanctuary will depend on the actions of the strongest vampire to ever exist, Kojou Akatsuki"--Back cover.

"Yukina has fallen in combat against homunculus Astarte, and it is Kojou Akatsuki--the Fourth Primogenitor, the boy she has been ordered to observe--who saves her. When Astarte attacks Yukina and Kojou with her terrifying Beast Vassal, Kojou is badly wounded, but what is happening to his body...?! The true power of the Fourth Primogenitor now comes to the fore!"--Back cover.

"Koju Akatsuki lives on the artificial island of Itogami, and has secret: He's the 'Fourth Primogenitor,' the most powerful vampire in the world. He's carefully kept this dark knowledge from his family and friends, but one day, a beautiful girl named Yukina Himeragi appears before him and tells him that she knows who he really is--and that she's been sent to... kill him?!"--Back cover.