"Haruna no Himitsu Mite Kudasai" is a manga series that centers around Haruna, a high school girl who harbors a peculiar secret: she has the ability to transform into a cat. This transformation occurs involuntarily, often triggered by stress or strong emotions, and she struggles to keep this ability hidden from her classmates and friends. The story explores her daily life as she navigates the challenges of maintaining her secret while dealing with typical teenage experiences, such as friendships, schoolwork, and budding romantic feelings.

Haruna's life becomes more complicated when a classmate, Takumi, accidentally discovers her secret. Takumi, initially shocked, decides to help Haruna keep her ability hidden, and their relationship gradually deepens as they spend more time together. The narrative delves into their growing bond, as well as the humorous and sometimes tense situations that arise from Haruna's unpredictable transformations. The series balances lighthearted moments with themes of trust, self-acceptance, and the complexities of human relationships.

The supporting cast includes Haruna's close friends, who remain unaware of her secret, and other classmates who add depth to the school setting. The interactions between characters are a key focus, highlighting the importance of communication and understanding in overcoming personal challenges. The story progresses through a series of episodic events, each contributing to Haruna's character development and her journey toward embracing her unique identity. The manga maintains a blend of comedy, romance, and slice-of-life elements, creating an engaging and relatable narrative.