Sixteen year old Ema Asano, a high school student and the daughter of deceased police officers, lives in Tokyo with her older sister Yuko. When Yuko fails to return home from a work party, Ema uses a GPS tracker on her sister's phone to track her down. The search leads Ema to a startling scene where she finds her unconscious sister in the arms of a man who appears to be a vampire, locked in combat with a werewolf. The vampire is Tamaki Utsunomiya, the CEO of an interior design firm called Topos, and the werewolf is Taiga Wakaki, his employee and a craftsman for the company.

Ema discovers that Tamaki, who is actually a 300 year old vampire from a species that calls themselves Aeternitas, and Taiga are vestiges of a major battle that took place between werewolves and vampires in West Germany nineteen years ago. For years, they have been hiding their supernatural identities and coexisting secretly within human society, with Tamaki typically using his ability to erase human memories when they are discovered. However, this power does not work on Ema. Unable to simply remove her from the situation, Tamaki instead opts to hire Ema and her sister, keeping them close to control the situation. Despite the ancient and violent feud between their kinds, the two supernatural beings find themselves forced to navigate their relationship under the watchful eye of the determined teenager, who announces she intends to keep them from killing each other. The story unfolds in the shadows of modern Tokyo, where Ema steps into a perilous hidden world that challenges her beliefs about justice and reshapes her destiny.