Sublimation

The novel takes place in a world where "instancing," the physical duplication of a person, occurs when someone crosses a border with the deep, often unconscious knowledge that their departure is permanent. Both the original and the duplicate are called "instances." Reintegration, the collapsing of two instances back into one person, happens through skin-to-skin contact and does not require mutual consent. A commercial wristband called the MERGEBREAK, manufactured by the tech company Mergebreak, disrupts the physical resonance between instances and prevents accidental reintegration. Interspersed throughout the narrative are expository passages drawing on Korean folktales, Homer's Odyssey, the Book of Genesis, and the Korean folk song "Arirang" to provide mythological and historical context for instancing.

Soyoung, a business analyst in Seoul engaged to her college boyfriend Taehyung (Tae), waits in a department store basement for her American instance, Rose. The two instanced when they were 11 years old, when their mother moved them from Korea to the United States, and they have never spoken since. Soyoung recently called Rose to tell her that their grandfather, Harabeoji, has died, and Rose agreed to come to Seoul for the funeral. Soyoung carries a spare MERGEBREAK wristband and is accompanied by her childhood friend Yujin, who also has an instance named YJ living in New York and working at Mergebreak.

Rose, a software engineer in Brooklyn, arrives exhausted and emotionally guarded, considering herself a "vestigial limb" of her Korean family. When the instances meet, Soyoung is surprised by Rose's American accent and coffee preferences. Rose straps on the MERGEBREAK with visible relief, which stings Soyoung. Over dinner with their cousin Minsoo and Tae, Rose learns from Minsoo that Harabeoji's dying wish was for the two instances to reintegrate, a detail Soyoung had withheld. Minsoo also gives Rose a manila envelope containing an inheritance.

The envelope reveals a deed to Harabeoji's house, where both instances grew up, granted to Rose or to the future reintegrated self but not to Soyoung alone. Soyoung is furious and walks away without explanation. The next morning, Rose wanders Seoul and ends up outside the house, where Soyoung's mother, the Korean instance of Rose's own mother, emerges and speaks with her briefly in a cordial but distant encounter.

Over the following days, the instances begin to bridge their gap. Soyoung brings Yujin along for moral support, and Rose eventually confronts Soyoung about the reintegration request. They agree the dying wish was unfair. At the burial, Soyoung erupts in a protective shout on Rose's behalf before storming off to the car, where she removes her MERGEBREAK and confesses the truth: She has always wanted to reintegrate. She envied Rose's life, wondered about her at every milestone, and wants to know what it feels like to have been the one to leave. She holds out her bare hand. Rose gives a measured refusal, explaining that reintegration will not fix anything and that she cannot bear the loss of two homelands. Soyoung reaches for Rose's hand anyway, and they reintegrate.

The reintegrated Soyoung-Rose struggles with doubled memories, cognitive dissonance, and nausea. Her relationship with Tae deteriorates because she no longer feels the warmth Soyoung once felt for him. She resolves to declare Korean citizenship until she sees a television broadcast: Mergebreak has announced "Mitosis," a product that can reverse reintegration within six months. YJ appears on screen as part of the leadership team, and Soyoung-Rose asks Yujin to arrange a meeting.

In New York, YJ has been promoted by Drew Thorsson, Mergebreak's COO, to oversee the Mitosis project after his previous boss, Megan, quit. YJ is navigating immigration anxieties tied to his H-1B1 work visa; he and Yujin have spent years pursuing dual citizenship so they can eventually reintegrate and travel freely between countries without triggering Korea's mandatory military service obligations. Soyoung-Rose flies to New York using Rose's passport without declaring her reintegration, reveals her situation to YJ, and asks for access to the Mitosis trials. YJ hesitates but eventually agrees to add her to a research study. The two begin spending time together and share a kiss born of mutual loneliness.

During the trials, each passage through the Mitosis gate produces vivid parallel memories from both lives, leaving Soyoung-Rose nauseated. She suspects she has been placed in a different trial than the one YJ intended. Meanwhile, Megan, who now works for Instancing Immigration Services (IIS), visits Yujin in Korea and gives him a USB drive containing classified Mitosis data. Yujin discovers the technology can prevent instancing entirely, force reintegration remotely, overwrite one instance's memories with another's, and create partial blends at any ratio. It can be installed in freestanding gates, fences, and lampposts. Yujin sends the USB to Soyoung-Rose, who shares the files with YJ.

At a meeting Soyoung-Rose engineers, Megan reveals the full picture: IIS plans to install Mitosis gates at border crossings before the public release, and Mergebreak will later sell full-capacity machines to approved governments. Megan wants YJ to leak this information to oust Drew and take his position. Soyoung-Rose believes the information should be released immediately, arguing that no single entity should control instancing. YJ prefers working within the system, fearing personal consequences. When YJ confronts Drew, Drew reveals he knows about Soyoung-Rose's illegal presence and uses it as leverage. Soyoung-Rose decides YJ will never act boldly enough.

She formulates a plan: steal YJ's keycards, break into the Mitosis lab, download the data, use the gate to separate herself, and release everything publicly from Korea. To distract YJ, she calls Yujin and reveals what she has been withholding: YJ does not actually want to reintegrate. Devastated, Yujin resolves to confront YJ in person. Soyoung-Rose visits YJ's apartment, steals his keycards while he makes tea, and sleeps with him before leaving.

That night, Soyoung-Rose breaks into the Mergebreak building and begins downloading files and calibrating the Mitosis gate. Yujin flies to New York and lets himself into YJ's apartment to force reintegration. YJ wakes in terror, and they struggle before Yujin manages to make contact. The combined Yujin discovers the missing keycards and races to the lab, smashing through a glass door with a fire axe.

Inside, Soyoung-Rose has set the gate's field to maximum radius. Yujin steps in despite her warnings and collapses. She runs to catch him and enters the field herself. Their consciousnesses merge inside a dreamlike reconstruction of Harabeoji's house, where Soyoung, Rose, and Yujin exist as separate entities. They argue about Mitosis, but Yujin admits the status quo is unacceptable. Rose proposes a compromise: Let her take the data and leave. Yujin does not have to be the whistleblower; he just needs to give her a head start. He agrees.

They emerge from the field as separate people. Rose declares she wants to keep their grandfather's house, and Soyoung agrees. Rose uses her technical skills to scrub their fingerprints from the server. Then, by mutual choice, Rose takes Soyoung's hand and they voluntarily reintegrate. Soyoung-Rose kisses Yujin goodbye and departs.

Alone, Yujin realizes the Mitosis gate can be disassembled. He unscrews the prototype, tapes it to his body, and brings it to Soyoung-Rose's apartment, asking to be separated into whatever versions would be most useful. Using the prototype, she splits Yujin in two: one to accompany her and one to remain at Mergebreak.

In the epilogue, a man and a woman board a plane carrying backpacks, a cat carrier, and checked luggage containing the dismantled gate. After takeoff, an avalanche of files hits every newsroom and forum. Six miles away, the version of Yujin who stayed behind sits at his desk in the Mergebreak office, refreshing his newsfeeds. The headlines drop. The world changes.