The Fourth Primogenitor—That's the world's strongest vampire that should only exist in legends. Accompanied by twelve Kenjuu and spreading calamity, this phantom vampire appeared in Japan. For the observation and obliteration of this Fourth Primogenitor, the government and Lion King decided to dispatch an attack mage known as a Sword Shaman. However, for some reason, the one chosen for the observation was a apprentice Sword Shaman girl, Himegari Yukina. Wielding the strongest anti-primogenitor spirit spear, Yukina arrived at Demon District, Itogami City. What is the true identity of the Fourth Primogenitor, Akatsuki Kojou, she encountered over there!? 
(Source: Baka-Tsuki, edited)

He never asked for this power.
 
Kojou Akatsuki used to be an ordinary high school boy--but that wasbefore 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 artificial island populated with all manner of demonic individuals, each with their own designs on the Fourth Primogenitor--?!
 
(Source: Yen Press)

Rin Tsukishima