He never asked for this power. Kojou Akatsuki was once an ordinary high school boy—but that changed when he became the Fourth Primogenitor, the most powerful vampire in history. To make matters worse, he has no recollection of how it happened. Meanwhile, middle schooler Yukina Himeragi is the Attack Mage assigned to monitor him—and to neutralize him if he loses control. But was it truly wise to send a cute girl to watch over a massively powerful vampire boy whose abilities trigger whenever he gets aroused? And all this on an artificial island filled with various demonic individuals, each harboring their own schemes regarding the Fourth Primogenitor—?!