"Horimiya" centers on the lives of two high school students, Kyoko Hori and Izumi Miyamura, whose seemingly contrasting personalities and social lives intersect unexpectedly. Hori is a popular, outgoing girl admired by her peers, while Miyamura is a quiet, reserved boy who appears unremarkable at school. However, their true selves are revealed when they meet outside of school: Hori is a responsible older sister who takes care of her younger brother and manages household chores, while Miyamura is a heavily tattooed and pierced individual with a hidden, more expressive side. This duality forms the foundation of their relationship as they grow closer.

The narrative explores their evolving bond, transitioning from friendship to romance, while addressing themes of self-discovery, acceptance, and the complexities of teenage relationships. Supporting characters, such as Hori's childhood friend Toru Ishikawa and Miyamura's friend Yuki Yoshikawa, add depth to the story, each grappling with their own insecurities and feelings. The series balances lighthearted, comedic moments with poignant reflections on identity and emotional vulnerability.

As the story progresses, Hori and Miyamura navigate the challenges of high school life, including misunderstandings, jealousy, and the pressures of societal expectations. Their relationship deepens as they learn to trust and support each other, revealing their flaws and strengths. The manga also delves into the lives of their friends, creating a rich tapestry of interconnected relationships and personal growth. Through its exploration of love, friendship, and individuality, "Horimiya" presents a heartfelt and relatable portrayal of adolescence.