Strike the Blood, Vol. 2 (light novel‪)‬

The friend of my friend is my enemy?!
Akatsuki (an ordinary high school boy and incidentally the world's mightiest vampire) is finally getting used to daily life with Yukina Himeragi, the attack mage whose job it is to observe him. But his peaceful life is interrupted by the appearance of Dimitrie Vattler, an envoy from the European primogenitor known as the "Lost Warlord." Vattler's enough of a problem, but it turns out he's got his own watcher, who's friends with Yukina--and who wants Kojou dead. Worse, their arrival is only the prelude to the emergence of a dark conspiracy that threatens the entirety of Itogami Island!