Vampires turn to ash in sunlight, so a young vampire named Yura Toraki has adapted to modern life by working the graveyard shift at a convenience store in Ikebukuro. He lives in a sunless semi-basement apartment with blackout curtains and tries to live an honest, peaceful life in hopes of one day becoming human again. This careful routine is shattered when he rescues a blonde woman from a drunkard, only to discover she is Sister Iris, a nun belonging to an order of vampire exterminators. To his horror, his natural enemy ends up as an unwanted guest in his home.

Yura is not a typical predatory vampire. He was turned against his will by a woman named Aika seven decades ago and has spent those years searching for her, hoping to reverse his condition. His life involves mundane concerns like comforting his divorced store manager and ordering online blood from soft-shelled turtles. Sister Iris is a member of the Dark Cross Knights, but she is not strictly by-the-book. After witnessing Yura sacrifice himself to ash to protect her from other vampires, she collects his remains and helps him revive, recognizing that not all phantoms are evil.

The central narrative follows the unlikely alliance between Yura and Iris. As they begin to live together, their relationship develops from forced cohabitation into a partnership. Together, they confront other phantoms and malicious vampires in modern Tokyo. A major arc involves their confrontation with Muroi Aika, the ancient strigoi who originally turned Yura. This leads to a climactic battle aboard a ship called the Mary I, where Yura uses a special Blood Seal created by a human ally named Miharu to restore his full power.

Despite their differences, Yura and Iris grow to rely on each other. Iris helps restore Yura’s fading hope and desire to fight, while Yura provides Iris with a connection to the supernatural underworld of Japan. The story blends slice-of-life comedy with supernatural action. In a final twist, after their initial adventures conclude, Iris does not return to her order. Instead, her superiors assign her to monitor Yura permanently, and she moves into the apartment directly next door, ensuring their chaotic partnership is far from over.