On an April night in Tokyo, university student Kakeru Sorano meets Koharu Fuyutsuki at a welcome party. She is a beautiful, warm young woman who laughs often and stands out from the crowd, a stark contrast to Kakeru's own introverted nature. What he does not initially realize is that Koharu is blind. Despite losing her sight to an illness, she has not given up on life, attending university classes, making friends, and dreaming of one day launching fireworks into the sky.

Kakeru, who carries trauma related to human relationships and has shut himself off from others, finds himself drawn to her. After he returns her dropped white cane following a class, the distance between them begins to shrink. As they spend more time together, Koharu reveals her list of things she wants to do, with setting off fireworks at the top. Though she cannot see them, the act of creating a brilliant, fleeting moment of light in the darkness becomes a powerful shared goal. For Kakeru, helping her pursue this dream becomes a way to start moving forward in his own life, motivated by the girl who has always been by his side despite her own struggles.

Their relationship deepens, and Kakeru learns that Koharu's condition is more severe than just blindness. Her illness is terminal, and she has only a limited time left to live. When she discovers this, she tries to push Kakeru away, asking him to forget about her to spare him the pain of her impending death. Kakeru refuses to accept this, struggling with the harsh reality but determined to stay with her. The narrative follows their emotional journey as they face this crisis together, from the joy of their first kiss to the despair of hospital visits and the fight to fulfill their promise of watching the New Year fireworks festival, even as Koharu's condition worsens and she suffers a collapse. The story is a delicate romance about two people searching for light—a girl who cannot see and a boy who has closed his eyes to the world—and how their connection forces them to confront loss, hope, and the value of living in the present moment.