During a routine class, Nishikata frets about the rain after leaving his umbrella at home, a small worry that opens up a day of playful teasing from Takagi. She nudges him by drawing the “umbrella” portion of aiaigasa, only to reveal a fish bone — a cheeky reminder of their inside jokes. After school, they pass the time with guriko, a traditional game, and Takagi clinches the win after nudging Nishikata about kissing her as a humorous punishment if he ever loses at scissors. The morning after, Nishikata and Nakai spot Kimura in the act of snapping pictures of Takao as part of documenting their daily school life before graduation, a quiet piece of memory that feels suddenly valuable. Tanabe-sensei politely reminds Kimura and Takao to treat these photos with care, underscoring how small moments can become lasting mementos.
In the next chapter, a swimming class becomes a playful arena for a new kind of competition: Nishikata challenges Takagi to see who can stay underwater the longest. She wins with a remark that he reads in a way that amuses and confuses him at once, a classic miscommunication that deepens their bond. The day’s mood shifts when Takagi learns from Mano about a rumor that wishing can be granted by glimpsing fireflies, a fantasy that threads through their summer plans. After the swim, Hamaguchi asks Nishikata to step in and help with the island’s mushi okuri, a task meant to give him a chance to spend time with Houjou before she leaves for Canada for summer school. Nishikata then invites Takagi to join, but the two find themselves unable to locate any fireflies despite their efforts.
As summer break begins, Mina Hibino and Yukari Tenkawa learn that Sanae Tsukimoto is aiming to continue high school in a city, and Mina ambitiously compiles a list of 100 activities the trio can tackle during the vacation. The days blur into small adventures as they stumble upon an abandoned kitten at a shrine. They bring the tiny creature to a pet store run by Ota, along with her parrot Katsuo, hoping to secure food and care. The kitten seems to approve of flowers, and the pair finally agree on the name Hana. Throughout their break, Takagi and Nishikata visit Hana at the shrine, showering her with attention and kindness. Sometime later, Takagi shares her decision to adopt Hana, and the two buy a flower-patterned collar as a gift. But when they return to the shrine, they discover a family preparing to take Hana with them. Nishikata comforts Takagi and pledges to keep her happy forever, a promise that anchors their growing commitment.
A festival later on offers a bit of reassurance: Mina and Yukari feel relieved that Sanae plans to stay on the island to continue high school with them. As fireworks light up the night sky, Takagi reiterates her vow to make Nishikata happy forever, a sentiment that carries into the hopeful postlude. In the post-credits scene, an adult Takagi and Nishikata share a life together with their daughter Chi Nishikata, as they join in mushi okuri and manage to find fireflies, closing the film on a tender note about family, memory, and small wonders that linger long after the school bell rings.
