The film opens with Haruki, who visits the hospital to get his stitches removed. During this visit, his attention is drawn to a diary left nearby. Upon opening it, he discovers it's Sakura's diary titled Living with the Dead, which reveals her struggle with a terminal pancreatic illness. Just as Sakura arrives and notices him with the diary, Haruki feels the weight of her situation but doesn't have anyone to share this truth with, rendering it somewhat inconsequential for him. After returning the diary, he witnesses Sakura's smile, which leaves a lasting impression.
As the story progresses, Sakura unexpectedly encounters Haruki on his way home, prompting him to change direction out of unease. However, Sakura cheerfully follows him, trying to initiate a conversation and requesting that he keeps her illness under wraps. Haruki admits to her that he lacks friends, but Sakura insists, saying, "I can spend the rest of my life with you." He dismisses her, yet she laughs it off, bidding farewell.
A week later, Sakura becomes a library assistant at the same place where Haruki works. She shares her diary with him, revealing a list of things she desires to accomplish before her time runs out, and she pleads for him to join her. Reluctantly, Haruki agrees, and they soon find themselves dining together at a restaurant. During their meal, Sakura inquires why he keeps to himself at school. Haruki explains that, outside of family, most consider him boring, yet Sakura expresses genuine interest in him, which continues to draw them closer.
The plot thickens when Sakura witnesses a man harassing an elderly lady. Boldly, she confronts him, but he reacts violently, grabbing her collar. She fights back, kicking him, and the two flee the scene together. Arriving at a café, Sakura requests Haruki's phone number, but he declines, asserting that he isn't ready for that kind of connection. Still, Sakura declares, "I will be your friend until I die," which Haruki reluctantly accepts.
Back at home, Haruki receives a message from Sakura expressing joy about their day and hoping he will remain in her life. The next day at school, rumors swirl about their growing bond. As Sakura arrives, her best friend Kyoko warns her that Haruki isn't her type. Unfazed, Sakura insists that their friendship is what matters most. Later, at the beach, Sakura reveals her fears about being open with Kyoko regarding her illness, as she believes it would invoke pity.
As summer vacation begins, Haruki and Sakura embark on a journey together, discussing their dreams and desires. Sakura asks for his first name, which he hesitates to divulge, wary of what it might mean for the future. Eventually, they share laughter and joys while shopping and having fun. One night at a hotel, as they engage in a game of truth or dare, Sakura's direct question about Haruki's feelings takes him by surprise, leading to an unexpected moment of connection.
But the mood shifts when they playfully test boundaries. After a series of heartwarming moments, Sakura asks about his fears concerning mortality, and Haruki hesitates, recalling the numerous medications he found in Sakura's bag. Later, Kyoko warns Sakura about the risks of getting too attached to Haruki, expressing her fears about her friend's delicate condition.
In what seems like a carefree scene at Sakura's home, she playfully expresses her desire for Haruki to treat her more like a girlfriend. The atmosphere shifts when they share a kiss, which startles Haruki, causing him to run away in confusion. Seeking clarity, Takahiro, another boy interested in Sakura, confronts Haruki aggressively, leading to a confrontation clouded with emotions and misunderstandings.
In the end, Sakura finds Haruki after the scuffle, their bond growing despite the chaos around them. She insists that their meeting was fate and pleads for him to remain at her side for whatever time they have left together. The movie concludes with Haruki learning to navigate his feelings while dealing with the reality of Sakura's condition and their fleeting moments together.
