On an April night in Tokyo, a university freshman named Kakeru Sorano is dragged by his roommate to a welcome party. There he meets Koharu Fuyutsuki, a girl who laughs often and speaks of her dreams with a warmth that stands in stark contrast to his own introversion and trauma related to human relationships. Kakeru soon discovers that Koharu is blind, a condition she developed due to an illness, yet she has not given up on anything. She attends university daily, shows interest in clubs, makes friends, and carries a bookmark written in Braille listing things she wants to do in life.

Despite his reluctance to form deep bonds, Kakeru finds himself drawn to help Koharu, starting by picking up her white cane after class. The distance between them begins to shrink as he becomes a quiet support for her on campus. While Kakeru is touched by her positivity and determination, Koharu is equally drawn to the young man who treats her frankly and does not look away from her disability. Central to their bond is Koharus dream of launching fireworks, a wish that puzzles Kakeru since she cannot see them, yet it becomes the light he gazes at directly for the first time, motivating him to move forward for the girl who is always by his side.

Their relationship deepens with the support of friends, including Kakerus cheerful and outspoken roommate Ushio Narumi and Koharus close friend Yuko Hayase, who is also Kakerus childhood acquaintance. However, the story takes a poignant turn as changes begin to occur in Koharus body. The group later learns she has been hospitalized, and Kakeru discovers the harsh truth that she has only six months left to live. Asking him to forget about her, Koharu says goodbye, leaving Kakeru to struggle for an answer in the face of sudden and devastating reality. Despite this, she promises to go to the New Year fireworks festival with him and pursues rehabilitation with all her strength, leading to a delicate and emotional story of two people searching for light in the darkness.