"At Full Moon" is a manga series that blends elements of romance, fantasy, and music, centering on a young girl named Mitsuki Kouyama. Mitsuki, a 12-year-old with a passion for singing, suffers from a throat tumor that prevents her from pursuing her dream. Despite her condition, she remains determined to become a professional singer, inspired by her childhood friend, Eichi Sakurai, who moved to America and promised to reunite with her once she achieves her goal.

The story takes a fantastical turn when two shinigami, Takuto and Meroko, appear before Mitsuki. They reveal that she has only one year left to live due to her illness. However, Takuto, moved by Mitsuki's determination, offers her a temporary solution: a magical pill that transforms her into a healthy 16-year-old version of herself, allowing her to pursue her dream under the stage name "Full Moon." This transformation comes with a caveat—Mitsuki must keep her true identity a secret, and the effects of the pill are limited, reverting her to her original form after a short period.

As Mitsuki begins her journey as a singer, she faces numerous challenges, including rivalries, the pressures of the entertainment industry, and the emotional toll of hiding her true self. Her relationship with Takuto and Meroko deepens, with Takuto becoming a protective figure who struggles with his growing feelings for Mitsuki, despite the rules forbidding shinigami from forming attachments to humans. Meroko, on the other hand, harbors unrequited feelings for Takuto, adding a layer of emotional complexity to their dynamic.

Throughout the series, Mitsuki's unwavering determination and kindness touch the lives of those around her, including her manager, Masami, and fellow artists. Her journey is interwoven with themes of love, loss, and the pursuit of dreams, as she grapples with her impending mortality and the sacrifices required to achieve her goals. The narrative explores the tension between Mitsuki's dual identities—her fragile, youthful self and the confident, older version she becomes under the shinigami's influence.

As the story progresses, Mitsuki's connection to Eichi is explored further, revealing deeper layers of their relationship and the impact of his absence on her life. The series builds toward a poignant climax, where Mitsuki must confront the reality of her condition and the choices she has made, ultimately leading to a resolution that balances hope and heartbreak. "At Full Moon" is a heartfelt exploration of perseverance, love, and the fleeting nature of life, set against the backdrop of the music industry and the supernatural.