In the 16th century, Japan found itself overrun by terrifying creatures known as vampires, or demons. Among the brave warriors was Kiyomasa, a valiant samurai who rose to defeat these fiends, but tragically met his end at the hands of Onigen, the oldest of vampires.
Fast forward to the 1970s in Tokyo, we meet Saya, portrayed by Gianna Jun, a unique being—a 400-year-old half-human, half-vampire. She dedicates her life to hunting down vampires, trained by Kato, a mentor who imparted survival skills, while also being loosely tied to an organization called "The Council". This secret society has long been dedicated to eradicating the vampire threat, but for Saya, her motives run deeper than mere duty: she seeks vengeance for her father, who was murdered by none other than Onigen (played by Koyuki).
For her upcoming mission, Saya must blend in undercover at Kanto High School, located on an American airbase near Fussa. Recently, there have been strange and suspicious deaths linked to vampiric activity, prompting her investigation to dig deeper into these incidents. When she first appears in class, her striking presence quickly ignites jealousy from a fellow classmate, Sharon. Compounded by this tension, Alice McKee (Allison Miller), the daughter of the base's general, also struggles with the spotlight, yearning for a taste of normalcy amidst the chaos.
Following a Kendo practice session encouraged by her instructor, Powell (played by Colin Salmon), Alice soon finds herself tormented by Sharon and her companions, who brandish sharp katanas and mock her. Just in the nick of time, Saya arrives, preventing Sharon from inflicting serious harm on Alice. However, Alice witnesses an unnerving scene through the door’s grill: an encounter that reveals that Sharon and her cronies are, in fact, vampires in disguise.
In a pivotal meeting, Michael, the leader of The Council, urges his team to proceed with caution as he uncovers vital evidence related to a plane crash in the mountains—evidence of Onigen's wicked work. As tensions rise, Alice’s father remains skeptical of her claims regarding the creature’s existence, even as the Council's clean-up crew finds themselves entangled in a web of deception orchestrated by officials.
Determined to uncover the truth, Alice investigates a local bar usually frequented by her Kendo instructor. There, horror strikes as she realizes that the establishment is a nest of vampires. Once more, Saya comes to her defense, battling the surrounding hordes. In a climactic showdown, Alice teams up with Saya, confronting Powell, and they eliminate him to protect themselves.
General McKee, unaware of the sinister operations of "The Council," begins probing deeper but soon becomes a victim when he learns too much. Just before his passing, he reveals to Alice the whereabouts of Saya. With her father gone, Alice, desperate and alone, seeks out Saya, who, despite her independence from The Council, takes on the responsibility of protecting her.
As the Council escalates their pursuit of Alice, a dangerous conflict unfolds, leading to the death of Michael at the hands of Luke, his ambitious deputy. In the chaos, Saya confronts her dark past, sharing with Alice the tragic history of her existence—including falling in love only to be burdened with the guilt of having killed her lover. With Kato perishing while saving her from Onigen, Saya fully embraces her purpose: to eliminate the demon that haunts her soul.
In their quest, Alice makes a harrowing sacrifice to save Saya, feeding her her own blood to heal. United, the duo ventures into the mountains, hoping to confront Onigen once more. They face peril as they are thrown from the road into a ravine during an attack by a demon.
Upon regaining consciousness, they find themselves in Ancient Japan, where past memories resurface. In a moment of revelation, Onigen unveils herself as Saya's mother, leading to a fierce confrontation between the two. Ultimately, Saya emerges victorious, slaying Onigen, though Alice is severely injured in the encounter.
Afterwards, we see Alice waking up post-accident, surrounded by paramedics, but her mind races with fragments of the nightmarish events. During a debrief, she tries to relay the truth about vampires and the Council, yet her claims fall on deaf ears. When asked about Saya's whereabouts, Alice cryptically states that she is "searching for a way back from the other side of the looking glass," leaving the truth shrouded in mystery and fear.
