After losing her brother and childhood friend Shuutarou to war and mysterious circumstances, Aoi Shirase clings to the hope of his survival, unaware of his transformation into a vampire. As Shuutarou joins a special military unit of supernatural beings to safeguard Tokyo, he crosses paths with Aoi, who has an unexplained connection to vampires. Bound by secrecy and a desire to protect Aoi from afar, Shuutarou grapples with the dilemma of shielding a loved one who wishes they were never separated.