Freelance photographer Kouhei Morioka travels to a castle in Germany to photograph paranormal activity for his friend Hiromi Anzai, an editor at an occult magazine. Upon entering the castle, he encounters a young girl in a white dress with cat ears who introduces herself as Hazuki. She shows a keen interest in Kouhei and offers him a kiss, but instead reveals herself to be a vampire, drains his blood, and turns him into her slave. To Hazuki's dismay, however, Kouhei remains unaffected by her bite. Hoping to escape the castle and her possessive butler Vigo, Hazuki forces Kouhei to assist her. With the help of his powerful exorcist cousin Seiji Midou, the two escape safely. Now free, Hazuki flees to Japan in search of her mother. Shortly after Kouhei returns home, he discovers that Hazuki has made her nest in his house, where he reluctantly allows her to stay. Meanwhile, other vampires set out to find the missing Hazuki. Equal parts gothic and adorable, Tsukuyomi: Moonphase is a charming and mystical story where two unlikely allies form a unique bond in an attempt to defy a society of immortals.