Strike The Blood Vol. 4

Kojo Akatsuki is, at first glance, an ordinary high school student at Saikai Private Academy on Itogami Island, a man-made island south of Japan that is a sanctuary for monsters and demons. However, there’s something different about Kojo: he is suspected of being a powerful vampire known as the Fourth Primogenitor who has the potential to disrupt the balance of power in the world!
Yukina Himeragi is an apprentice Sword Shamen from the Lion King Agency who is sent to observe Kojo and eliminate him should he prove to be a threat. Taking her role as observer very seriously (perhaps too much so), she moves into the apartment next to him and begins following him everywhere. However, she soon realizes there is more to the situation than she first thought, and unbeknownst to her, there are threads of fate that bind them together as she eventually begins to develop feelings for him in this supernatural action manga by Gakuto Mikumo and Tate.
In Vol. 4, Kojo and Yukina attend a yacht party at the invitation of Dimitrie Vatler, but things soon turn serious when they uncover a terrorist plot that threatens the whole island!
Notice: This manga is written in Japanese.