"Koi Shitagari no Blue" centers on the lives of two high school students, Haruto and Yui, whose paths cross in unexpected ways. Haruto, a reserved and introverted boy, harbors a deep passion for music, particularly the blues. He spends most of his time practicing his guitar, finding solace in its melodies. Yui, on the other hand, is outgoing and cheerful, known for her vibrant personality and love for dancing. Despite their contrasting natures, they share a common thread of longing—Haruto for a connection beyond his music, and Yui for a sense of purpose beyond her carefree exterior.

Their relationship begins when Yui stumbles upon Haruto playing his guitar in an empty classroom. Intrigued by his music, she insists on forming a band, believing their talents could complement each other. Reluctantly, Haruto agrees, and the two start collaborating, blending his bluesy guitar riffs with her rhythmic dance moves. As they work together, their bond deepens, revealing vulnerabilities and insecurities they had kept hidden. Haruto struggles with self-doubt about his musical abilities, while Yui grapples with the pressure to maintain her cheerful facade despite personal struggles.

The narrative explores their evolving relationship, alternating between moments of camaraderie and tension. Their creative partnership becomes a catalyst for personal growth, as they confront their fears and aspirations. Supporting characters, such as their classmates and bandmates, add layers to the story, providing both encouragement and challenges. Themes of self-discovery, artistic expression, and the complexities of human connection are woven throughout the series, creating a poignant and relatable tale.

As the story progresses, Haruto and Yui face pivotal moments that test their resolve. Competitions, misunderstandings, and external pressures force them to reevaluate their priorities and the strength of their bond. The manga balances lighthearted moments with emotional depth, capturing the nuances of adolescence and the transformative power of shared passions. Through their journey, "Koi Shitagari no Blue" paints a heartfelt portrait of two individuals finding their voices and learning to harmonize their lives, both on and off the stage.