The protagonist, a vampire named Marx, arrives in Tokyo, Japan, after leaving France. He is an ancient being who has lived through Japan's Sengoku period and is fascinated by its modern transformation, particularly its advancements in technology and culture, fueled by his love for manga and anime. Upon arrival, he experiences "human intoxication" due to the overwhelming number of people in Shibuya and is helped by a kind Japanese doctor, Yuki Kashiwagi.
Yuki takes Marx to her clinic, where he undergoes a brief examination. He admits to feeling hungry, which is a euphemism for his need to feed. After sharing a meal with Yuki and her staff, Marx is drawn into a police investigation when Yuki is called to a crime scene. He uses his mind-influencing abilities to join them, revealing his hidden medical license. At the scene, they discover a victim with their liver missing, a gruesome act that Marx recognizes as non-human. He predicts such incidents will increase, alarming the police and Yuki.
Later, Yuki invites Marx to tour Tokyo with her and her clinic's nurses, Mana and Mika. During the tour, Marx discreetly feeds on a woman in a department store, using a memory-wiping kiss to avoid suspicion. They visit the Skytree and Asakusa, where Marx learns more about the women's lives and their struggles with relationships. He also begins to develop feelings for Yuki, which he struggles to reconcile with his vampiric nature.
Marx also contacts his friend Rick, another vampire, who advises him to embrace his feelings for Yuki, suggesting he could turn her into a vampire if he fears losing her. Meanwhile, Marx continues his work as a doctor at a university hospital, where he excels as an interpreter due to his multilingualism. He struggles with his growing attraction to Yuki, especially after a night where he gets drunk and she takes care of him, leading to an awkward morning where he realizes he might have feelings for her.
A significant turning point occurs when Marx encounters another vampire, a descendant of his own lineage, who leads him to a "feeding ground" where women willingly offer themselves to be fed upon. This encounter allows Marx to satisfy his immediate bloodlust but also introduces him to other vampires in Japan and the existence of werewolves causing trouble. He also learns that Yuki has been called to another crime scene with a similar victim, raising concerns about their secret identities being exposed.
Marx's internal conflict intensifies as he grapples with his vampiric urges and his burgeoning affection for Yuki. He confides in Rick about his feelings, who encourages him to pursue them, offering solutions like turning Yuki into a vampire or erasing her memory if she fears him. Marx decides to try and face his feelings, despite his lack of confidence.
The chapters conclude with Marx experiencing severe hangovers and making mistakes at work, indicating his emotional turmoil is affecting his abilities. He receives a visit from Yuki, who brings him an IV drip to help him recover. During this time, he confesses his feelings for her, but a moment of near-succumbing to his bloodlust forces him to pull away. He is left contemplating his future and the difficult path ahead, torn between his immortal nature and his human emotions.