Keiki Kiryuu, a high school student, finds himself entangled in a peculiar situation when he discovers a love letter in his shoe locker. The letter, signed by a secret admirer who identifies only as "Cinderella," includes a pair of panties as a token of affection. Determined to uncover the identity of his mysterious admirer, Keiki begins to investigate the girls in his life, each of whom exhibits unique quirks and potential motives.

Among the suspects is Mao Nanjou, the student council president and a close friend who often teases Keiki but harbors a more serious side. Sayuki Tokihara, the class representative, is known for her strict demeanor and a hidden passion for erotic literature. Yuika Koga, a cheerful and athletic girl, has a playful personality but also a secretive side that Keiki finds intriguing. Mizuha Fujimoto, Keiki's younger sister, though seemingly innocent, occasionally displays behavior that raises questions. Lastly, Ayano Fujimoto, Mizuha's friend, is a shy and reserved girl who struggles with expressing her feelings.

As Keiki delves deeper into the mystery, he encounters various comedic and awkward situations, often driven by the eccentric personalities of the girls. The narrative explores themes of love, friendship, and the complexities of human relationships, all while maintaining a lighthearted and humorous tone. Each episode reveals more about the characters' backgrounds and motivations, gradually narrowing down the list of potential "Cinderellas."

The series balances its comedic elements with moments of genuine emotional depth, particularly as Keiki grows closer to understanding the true feelings of those around him. The interactions between the characters are central to the plot, with each girl's unique traits contributing to the ongoing mystery and the development of their relationships with Keiki. The story culminates in a resolution that ties together the various threads of the narrative, providing closure to the central mystery while leaving room for the characters' continued growth and interactions.