A 12-year-old tomboy named Eri Kasuga lives an ordinary life in a small Japanese town, balancing her playful, rebellious spirit with the typical routines of a sixth grader. Her world is turned upside down with the unexpected arrival of two aliens from the distant planet Mahl. The first is Chinpui, a resourceful, mouse-like creature with a fondness for ramen, and the second is Wandayuu, a talkative, dachshund-like being whom Eri often calls Grandpa Wanda. They bring her startling news: she has been chosen as a candidate to become the bride of their planet's unseen Prince Lulealv.

The core conflict of the story arises from Eri's forceful rejection of this predetermined fate. She is uninterested in an interstellar arranged marriage, especially when her affections lie with her studious but physically weak classmate, Uchiki Sho. The two aliens decide to remain on Earth, setting the stage for countless chaotic situations. While Chinpui becomes a genuine friend and ally, often using his reality-warping abilities to help her with daily problems, Wandayuu persistently, and often annoyingly, tries to convince Eri to accept her royal destiny, frequently with elaborate schemes that backfire.

The narrative of Chinpui Eri-sama no Good Luck focuses on this struggle between destiny and personal choice. Eri treasures her earthly life and her bond with Uchiki, but she is constantly pulled toward a future she does not want. The story explores her relationships with her classmates, including the wealthy rival Sunemi Koganeyama, as she navigates the chaos brought by the aliens. It balances comedic mishaps with deeper themes of autonomy and loyalty. The 2025 short film, created to commemorate the 40th anniversary of the original manga, brings this central dynamic back into focus. With Eri still defiant against the betrothal, the movie follows her ongoing resistance and her vibrant, complicated interactions with Chinpui as they face another series of extraordinary, everyday adventures.