Hiroko Watanabe [Miho Nakayama] lives in Kobe and loses her fiancé, Itsuki Fujii, in a mountain-climbing accident. Two years pass, and on the day of Itsuki’s memorial ceremony she pores over his high school yearbook, finding an address tucked under his name. She writes a letter to Itsuki and soon receives a reply from a woman named Itsuki Fujii, who bears a striking resemblance to Hiroko. The film unfolds as a dialogue between Hiroko and this Female Itsuki, with their correspondence weaving a quiet, introspective thread through both women’s lives.
Female Itsuki, who works at the public library, wrestles with a stubborn cold and refuses to seek medical help. It’s revealed that her father died of pneumonia while she was in high school, a detail that shadows her present life. Hiroko, moved by the letter, shares it with a friend she trusts, Akiba, [Etsushi Toyokawa], hoping for guidance. Akiba confesses his own feelings for Hiroko and encourages her to let go of Itsuki, even as he helps her hold on to memories.
As the letters continue, Hiroko and Akiba organically shift from being confidants to collaborators in a plan to uncover the truth. They decide to visit Otaru, Female Itsuki’s hometown, in an attempt to bring clarity to Hiroko’s doubts about the connection between the two Itsuki Fujiis. But on the way, Female Itsuki is tricked into going to a hospital, where she falls asleep and experiences a fever dream in which she relives her father’s death. Meanwhile, Hiroko and Akiba wait outside Female Itsuki’s home, choosing to leave a letter behind rather than meeting in person. They glimpse each other across a distance, and then part ways, each carrying their own sense of what they’ve learned.
Back at home, Hiroko confronts a startling possibility: there were indeed two Itsuki Fujiis in the yearbook, and perhaps her own striking resemblance to Female Itsuki helped draw her fiancé to her. She asks Female Itsuki to confirm this theory and to share memories of Itsuki from their high school days.
Flashbacks reveal the deeper history: Male Itsuki was shy and peculiar, and the two Itsakis were often paired as a couple by their classmates. Female Itsuki had tried to act as a go-between for Sanae, a girl who had a crush on Itsuki, but the effort didn’t quite succeed. During her father’s mourning period, Female Itsuki is visited by Male Itsuki, who asks her to return a book for him. After she returns to school, she learns that Male Itsuki has transferred, and that the book exchange was the last time she sees him.
Female Itsuki later visits her old school and learns that Male Itsuki died in the mountain accident two years earlier. Hiroko and Akiba make a pilgrimage to the very mountains where Itsuki died, sharing memories and a moment of quiet reverence. Akiba wakes Hiroko to watch the sunrise, pointing to a peak as if greeting Itsuki. Hiroko breaks into tears, calling out to Itsuki in a way that echoes the letters they’ve written to each other, while Female Itsuki awakens in the hospital.
Some time later, Hiroko and Itsuki (through the ongoing letters) continue their correspondence. Itsuki receives a visit from volunteer girls from her former high school library, who show her the book Male Itsuki had given her to return. They discover his name on the checkout card and, on the back, find a sketch he made of Female Itsuki. Rather than sending a reply about the drawing, Female Itsuki chooses not to write back, leaving the final moment open to memory, possibility, and the strange, tender tie between two women who share a name, a memory, and a past that refuses to be simply reconciled.
