Sumire meets Miu at a wedding and instantly falls in love with her for the first time in her life.

Sumire arrives at K's door with fashionable new clothes and a new haircut, barely recognizable from her usual self.

Miu persuades Sumire over a restaurant lunch to work for her company and begin Italian lessons.

K helps Sumire move into a new apartment and declines her dinner invitation, overwhelmed by desire for her.

Sumire sends K a five-page letter from Rome describing her all-consuming desire for Miu and her inability to write.

A second letter arrives from France: Sumire and Miu have accepted an Englishman's offer of his villa on a Greek island.

Miu calls K at two in the morning, tells him something happened to Sumire, and asks him to fly to Greece.

K takes a ferry to the Greek island and finds Miu at a café, who brings him to the villa over dinner.

Miu tells K that Sumire disappeared without a trace four nights ago, leaving all her clothes and shoes behind.

Miu recounts finding Sumire in a dissociative state on the floor and then Sumire's attempt to initiate sex.

Miu rejects Sumire's advances and reveals that a traumatic past event left her permanently unable to feel desire.

K searches Sumire's room, unlocks her suitcase using his zip code, and finds a floppy disk inside.

K reads both of Sumire's documents twice and realizes they share a single thread: references to another world.

K wakes to unexplained music, follows it outside, and momentarily feels his body and identity are no longer his own.

Sumire calls K in the night to say she is back, and both discover they are looking at the same half-moon.

K and Sumire are inseparable friends, but when Sumire meets the elegant Miu at a wedding she falls instantly in love and restructures her life to be near her. Letters sent from Europe hint at the consuming force of Sumire's desire, and then contact stops entirely when Miu calls K in the middle of the night asking him to fly to Greece. On the island Miu reveals that Sumire vanished without a trace the morning after Miu rejected her one attempt at intimacy, leaving all her belongings behind. K searches Sumire's room, finds hidden documents, and begins to suspect she may have crossed into another version of reality rather than died. He returns to Japan without answers, haunted by her absence, until one night the phone rings and Sumire herself is on the other end, asking him to come find her.

The headline events that drive the central mystery of Sumire's disappearance.

Sumire drops out of university to pursue writing while K graduates, earns his degree, and becomes a primary school teacher.

K begins a series of affairs with married older women as a way to manage his unrequited desire for Sumire.

At the wedding, Miu mistakenly calls Kerouac a sputnik instead of a beatnik; Sumire secretly adopts the name Sputnik Sweetheart for Miu.

Sumire calls K before dawn from a phone booth in the park to ask him to explain the difference between a sign and a symbol.

After their lunch, Miu brings Sumire to her apartment and gives her a wardrobe of elegant clothes to wear to work.

At a dinner, Miu grows serious and tells Sumire she is not a whole person after something that happened 14 years ago.

Sumire calls K late at night to confess she has completely lost the ability and will to write since meeting Miu.

When K meets Sumire for the second time since Miu entered her life, he once again barely recognizes how much she has changed.

While helping Sumire move, K assures her that he would remain her closest friend even if she were a lesbian.

Miu describes to K the strict peaceful routine she and Sumire followed each day during their first four days on the island.

K visits the beach where Miu and Sumire used to swim, swims nude, and dozes imagining Sumire's state of mind there.

Miu returns to the island from Athens with a Japanese embassy official and the police investigation finally becomes serious.

K and Miu say their farewells at the ferry dock; she tells him she likes him, and he watches until she disappears.

K's flight home from Athens is cancelled and he spends the night walking alone through the city's ancient ruins.

Back in Japan, K spots Miu in a car moving alongside his taxi but she never looks over and notices him.

Before Sumire vanishes, both she and K lead carefully isolated lives — K teaching school and managing unrequited desire through brief affairs, Sumire devoted to writing while neglecting nearly everything else. When Miu enters Sumire's world at the wedding, a small slip over a Russian satellite's name gives Sumire a private nickname for Miu and quietly signals the loneliness both will come to embody. Sumire's transformation unfolds through modest moments: new clothes delivered at Miu's apartment, hushed dinner revelations, and the gradual loss of her desire to write. On the Greek island, K tries to piece together what happened through Miu's account of their peaceful daily routine and his own solitary visit to the beach where the two women once swam. As the investigation stalls and K departs, he catches one last distant glimpse of Miu that confirms how thoroughly the world has already moved on without Sumire.

The supporting scenes that flesh out the world around Sumire's disappearance.

Sumire tells K that her love for Miu feels like a dangerous current she cannot resist, even knowing it may cost her everything.

Sumire formally accepts Miu's job offer at lunch, agreeing to work three days a week and take Italian lessons on the side.

Miu takes Sumire to restaurants to maintain business relationships and teaches her how to properly taste and order wine.

Sumire tells K she feels like a satellite drifting through space with no gravity and no sense of where she is headed.

K realizes during Sumire's move that his desire for her is identical to the desire she feels for Miu, equally unreturnable.

K waits days past Sumire's expected return from Greece before finally receiving Miu's phone call in the middle of the night.

Miu mentions during her account that she noticed Sumire had started writing again in the days just before she disappeared.

Sumire's first document reveals she stopped writing after meeting Miu because she could no longer think without writing first.

Sumire's first document describes a recurring dream in which her dead mother vanishes through a hole in a wall just out of reach.

Sumire's second document recounts Miu being stranded alone at the top of a Ferris wheel after the attendant forgot her.

Trapped on the Ferris wheel, Miu uses binoculars to watch a double of herself having sex with the man who had been following her.

Miu wakes in a hospital with completely white hair and a permanent sense that half of herself has crossed to another world.

K begins to wonder whether Sumire crossed to the other side of reality in search of the half of Miu that can still feel desire.

K drops the stolen security office key into a river and immediately feels his body grow lighter with relief.

K breaks up with his girlfriend on the drive home, realizing that when he said it was best for everyone, he was only thinking of Sumire.

Sumire's love for Miu is not merely romantic longing but a force that reshapes her identity — she accepts a job, learns a language, and describes her desire as a dangerous current pulling her toward an unknown destination. As she grows closer to Miu, she loses the ability to write, which for her means losing the ability to think, severing the core of who she is. The documents Sumire left behind reveal the depth of this internal crisis alongside Miu's own fractured past: a night alone on a Ferris wheel where she witnessed a double of herself having sex, an experience that split her permanently in two and turned her hair white. K reads these accounts and begins to theorize that Sumire followed Miu's lost half into another world, a theory reinforced when he briefly feels his own identity slip away in the darkness. Back in Japan, K gradually sheds the attachments tying him to his old life, beginning a slow and uncertain process of moving forward.