Luka Edelmondt Finsternis, a centuries-old vampire of noble bearing, is perpetually hungover and exhausted from his usual demon-world routines. Searching the human world for a change of pace, he stumbles upon the website of Full Moon Baths (Mangetsu no Yu), a traditional Japanese bathhouse that promises to melt away fatigue and rejuvenate even the creakiest bodies. Intrigued, he pays a visit, only to find that the bathhouse is short-staffed and struggling to stay afloat. The eldest son and heir, Sakura, is responsible for keeping the business running while also caring for his younger brother, and he has little patience for a pompous vampire who seems more interested in soaking than in following rules.

What begins as a one-time cure for Luka’s hangover quickly turns into a regular habit. He becomes a fixture at the bathhouse, using his otherworldly charm and aristocratic manners to inadvertently attract customers, while his inability to grasp human social norms creates constant comedy. Sakura, exasperated yet begrudgingly accepting, has to manage not only the bathhouse's daily operations but also the supernatural complications that come with a vampire in residence—particularly when Luka’s magic requires either Sakura’s blood or physical intimacy to stabilize in the human realm. This tension drives much of the humor, though the story never makes explicit what it teases.

The manga is structured as a lighthearted slice-of-life comedy spanning seven chapters in a single volume. Key narrative arcs include a summer festival where Luka helps draw crowds with his supernatural allure, a sports meet that pits human and vampire abilities against each other, and a humorous photoshoot that plays with traditional gendered roles. Beneath the slapstick, the story explores themes of found family and community warmth, as the bathhouse becomes a gathering place for a quirky ensemble that includes Sakura’s adorable younger brother Ume, his loyal dog Pequeño, a gruff but kind grandfather, and a cast of eccentric regulars. Luka’s haughty exterior gradually softens as he bonds with the humans, and Sakura learns to accept help from an unlikely source. The narrative concludes with the bathhouse’s fortunes improving and the relationship between the two leads left in a fond, unresolved space that hints at romance but refuses to commit to a label.