"Rizelmine" is a 12-episode anime series that blends elements of comedy, romance, and science fiction. The narrative centers around Tomonori Iwaki, a high school student whose life takes an unexpected turn when he is suddenly informed by his father that he must marry a mysterious girl named Rizel. Rizel is revealed to be a genetically engineered being created by a secret government organization, and her existence is tied to a classified project. Despite her childlike appearance and demeanor, Rizel is determined to fulfill her role as Tomonori's wife, leading to a series of comedic and chaotic situations.

Tomonori initially struggles to adapt to his new reality, as Rizel's naivety and eccentric behavior often clash with his attempts to maintain a normal life. Rizel's unwavering devotion to him, combined with her superhuman abilities, frequently disrupts his daily routine. The series explores their evolving relationship as Tomonori gradually begins to accept Rizel, though her antics and the interference of other characters continue to complicate matters. Supporting characters include Rizel's caretaker, Miyu, who oversees her well-being and ensures she adheres to her mission, and Tomonori's classmates, who become entangled in the bizarre circumstances surrounding Rizel.

The plot incorporates lighthearted humor, often derived from Rizel's misunderstandings of human customs and her exaggerated reactions to everyday situations. However, underlying themes of identity, purpose, and the ethics of genetic engineering occasionally surface, adding depth to the otherwise comedic tone. The series balances episodic comedic scenarios with a broader narrative thread involving the government organization responsible for Rizel's creation, which seeks to monitor and control her actions. As the story progresses, Tomonori and Rizel's bond deepens, culminating in a resolution that underscores their mutual growth and acceptance of their unconventional relationship.