College student Sorano Kakeru, who carries trauma related to human relationships, notices a woman quietly reading a book alone during one of his classes. One day, Kakeru is dragged into a class reunion by his dorm roommate, Narumi Ushio. Through his childhood friend Hayase Yuko, who is also at the reunion, he meets a blind woman named Fuyutsuki Koharu. She turns out to be the same woman he had seen reading in the classroom. There, Kakeru learns that Koharu is blind, and due to the circumstances, he ends up helping her with her classes.

Kakeru decides to support Koharu in her classes once again. To fulfill the second item written on Koharu’s bookmark, her “Things I Want to Do” list, “set off fireworks,” Kakeru and Koharu go out together to Asakusa. Koharu feels overwhelmed by the crowds, and Kakeru struggles to support her in the busy streets, but little by little, the distance between them begins to close. During this time, Kakeru finally asks about something that had been on his mind: the reason Koharu lost her sight. After opening up about her past, Koharu is deeply moved by Kakeru’s kindness, which comes not from pity but from treating her as an equal.

Kakeru is questioned by Yuko about his feelings for Koharu, while Narumi urges him on, saying, “If you let this chance slip, there won’t be another.” Lost in thought, Kakeru struggles to decide what to do. Meanwhile, Koharu, prompted by words from her mother Haruka, begins to face the feelings she had long kept buried deep in her heart. Soon, the four of them make plans to set off fireworks, one of Koharu’s wishes. On the day itself, thanks to Narumi’s arrangement, Kakeru and Koharu end up lighting the fireworks together, just the two of them. At the same time, Yuko, who goes along with Narumi’s suggestion, tries to seal away her hidden feelings for Kakeru. As night falls and the two spend quiet time together, the feelings between Koharu and Kakeru begin to accelerate.

On their way home after the fireworks, Koharu kisses Kakeru. But behind that moment of happiness, changes begin to occur in Koharu’s body. Meanwhile, Kakeru returns to his hometown with Yuko for the third death anniversary of his late best friend, Haruto. Haruto’s mother, too, has lost someone dear and remains unable to move forward. To her, Kakeru, who has begun to change after meeting Koharu, speaks words that reflect his growth. acing his past wounds and encouraged by Yuko, Kakeru makes up his mind and sends Koharu a video capturing the scenery of his hometown along with the words he once spoke there. However, soon after, contact with Koharu suddenly cuts off, and Kakeru is unable to see her again. On top of that, an unimaginably cruel turn of events awaits Kakeru.

After learning that Koharu, who had been out of contact, is in the hospital, Kakeru, Narumi, and Yuko rush to see her. In the hospital’s kids’ room, Kakeru finds Koharu playing the piano for children. When he speaks to her, she responds with, “Who are you?” and rejects him. From Koharu’s mother, Haruka, they learn that Koharu’s memory has become confused due to a certain reason, leaving them in shock. Meanwhile, Koharu spends her days volunteering in the hospital's kids’ room, playing the piano for the children. One day, determined to spend more time with Koharu even if she cannot remember him, Kakeru takes action. However, he soon learns that Koharu has been suffering under a reality far more painful than he ever imagined.

Koharu tells Kakeru that she has only six months left to live and asks him to forget about her, saying goodbye. Faced with this sudden and harsh reality, Kakeru cannot find an answer for what he should do. Narumi and Yuko find a flyer for a fireworks festival to be held after the New Year, hoping to do something for Koharu, who loves fireworks. Still, Kakeru remains lost, unsure of what the right choice is. Meanwhile, Koharu, not wanting to cause pain to the people she loves, begins to consider giving up on treatment altogether. At that moment, Kakeru remembers Koharu’s “yellow bookmark” and realizes that the “Things I Want to Do” list written on it is not finished yet. Once again, he starts running forward for Koharu’s sake.

Koharu, who promised Kakeru that she would go to the New Year fireworks festival with him, continues her rehabilitation with all her strength. At the same time, Kakeru struggles with doubt, wondering whether pushing Koharu forward when recovery seems unlikely might be irresponsible. One day, Kakeru is approached at the hospital by Miura, Koharu’s attending physician. He opens up about his uncertainty, and after hearing Miura’s words, Kakeru decides to stay by Koharu’s side no matter what. Meanwhile, Koharu works hard at her rehabilitation with the fireworks festival in mind, but feelings of anxiety and resignation begin to take root deep in her heart. One night, she lets her true feelings slip while talking to Yuko. As the fireworks festival approaches, Koharu, Kakeru, Narumi, and Yuko support one another while carrying their own feelings.

On the long-awaited day of the fireworks festival, Koharu’s condition suddenly worsens and she collapses. Thankfully, she regains consciousness. Despite having worked so desperately through rehabilitation for the sake of the festival, Koharu is devastated when she realizes she cannot go. Seeing this, Kakeru, with the help of Narumi and Yuko, carries out a certain plan in Koharu’s hospital room. It becomes a moment that feels almost miraculous. In that room, Koharu tells Kakeru for the first time another reason why she loves fireworks, one she had never shared before. Even if sight is lost, even if memories fade, the two believe that some things remain for certain. Holding onto that belief, Koharu and Kakeru move forward, wondering what kind of path lies ahead for them.