"Horimiya" centers around the lives of high school students Kyoko Hori and Izumi Miyamura, whose contrasting personalities and hidden sides form the foundation of the narrative. Hori is a popular, academically successful girl admired by her peers, while Miyamura is a quiet, seemingly unremarkable student who keeps to himself. Outside of school, however, their lives are vastly different. Hori takes on significant responsibilities at home, caring for her younger brother, Souta, and managing household duties due to her parents' busy schedules. Miyamura, on the other hand, reveals a secret side: he is heavily tattooed and pierced, a stark contrast to his reserved school persona.

The two meet unexpectedly when Souta is brought home by Miyamura after a minor accident. This encounter leads to the discovery of each other's hidden lives, fostering a unique bond built on mutual understanding and trust. As their relationship develops, the series explores themes of self-acceptance, vulnerability, and the complexities of adolescence. Hori and Miyamura navigate their feelings for each other while balancing their personal struggles and the expectations of those around them.

The supporting cast adds depth to the story, with characters like Toru Ishikawa, Hori's childhood friend who harbors unspoken feelings for her, and Yuki Yoshikawa, Hori's best friend who grapples with her own insecurities and romantic dilemmas. The interactions among the group highlight the nuances of friendship, love, and personal growth. The narrative also delves into the lives of other classmates, such as the cheerful but perceptive Remi Ayasaki and the reserved yet kind Sakura Kono, further enriching the high school setting.

Throughout the series, the evolving dynamics between Hori and Miyamura serve as the emotional core, portraying a realistic and heartfelt depiction of young love. Their relationship is marked by moments of humor, tenderness, and introspection, as they learn to embrace their true selves and support one another. The story balances lighthearted, comedic moments with poignant reflections on identity and connection, making it a relatable and engaging portrayal of teenage life.