Totsuko Higurashi is a high school student attending a religious boarding school in Nagasaki, who possesses a secret and unusual gift: she can see the emotional states of other people as vibrant, colored auras. From bliss and excitement to serenity, each feeling manifests as a distinct hue, though she is unable to perceive her own color. While she is often socially awkward and worries about causing dark feelings in others, she finds herself captivated by a classmate named Kimi Sakunaga, who glows with the most beautiful shade of blue she has ever seen.

When Kimi suddenly drops out of school under mysterious circumstances, Totsuko tracks her down to a used bookstore in a quiet corner of town. There, she discovers that the seemingly reserved Kimi is a budding guitarist. In a flustered moment, Totsuko lies and claims she can play the piano to stay close to her. Their conversation is overheard by Rui Kagehira, a gentle and quiet boy with a calm green aura who is passionate about music but faces family pressure to pursue a medical career instead.

Despite Totsuko's initial deception and the fact that she does not actually play an instrument, the three misfits decide to form a band. They find a sanctuary in an old, decommissioned church on a remote island, where they gather to practice. For Rui, who plays the theremin, and Kimi, who hides her departure from school from her family, this shared space becomes a refuge from their personal struggles. As they write songs and learn to play together, their music allows them to communicate feelings they cannot put into words, stirring deep friendships and subtle romantic affections. Through this creative bond, they begin to overcome the pain of conforming to expectations, the agony of bearing burdens alone, and the hardship of pretending to be someone they are not. The story culminates in their first live performance at the school festival, where the trio finally reveals their true inner colors to the world.