In 1877, Sen finishes burying a spy she killed. As she handles the man’s severed head, she thinks she hears it whisper a warning. Shaken, she disposes of the body and reflects on the certainty that the government will soon find and kill her family. After hiding the head, she retrieves Lee from under the porch, where he had been hiding, and leads him to a river to wash off the spy’s blood.

As they talk, Lee calmly asks how many people she has killed. When Sen answers, Lee reveals that he has also killed a man. Sen tells him her father refuses to flee their home, resigning them all to their fate. She refuses to abandon her father, even to save herself. They agree to again explore the spiritual connection between them and return to her room. There, Lee is stunned to see a painting Sen made of a woman he recognizes as his mother.

The painting of Lee’s mother triggers a flashback to his last day with her in Cambodia when he was 12. He recalls her sadness after they rescued a turtle whose shell had been permanently deformed by a plastic ring. She then told him she was going for a walk, and he never saw her again.

In the present, Sen explains that she sees his mother’s face in visions, standing on a beach as the ocean closes in. Lee, realizing Sen can connect with his mother’s spirit, insists she take him to this spiritual plane. Sen reluctantly agrees, and they hold hands, transporting back to the desolate, ashen shore. They approach a figure they believe is his mother, only to find it is a suitcase with screams coming from inside. Lee opens the case, but finds it empty. He and Sen begin dissolving into ash before they reappear in the room. Disappointed, Lee invites a shaken Sen to stay the night in his world, where she might feel safer. She agrees, and they fall asleep on his futon.

Returning to her own time at sunrise, Sen is met by Itaro, who unexpectedly tells her to get dressed for a trip into town. He commands her to leave her katana behind, an order that makes Sen fear he intends to sell her into marriage. They walk to a blacksmith’s shop, where her father presents her with a box containing a new, masterfully crafted katana.

Thinking it is a test, she assesses the blade and declares it perfect. Her father then reveals the sword is a gift for her. Outside, he explains with uncharacteristic warmth that she will need a weapon worthy of her skill when the imperial soldiers arrive. He expresses his deep faith in her as a warrior, calling her soul strong and pure. Sen is overwhelmed by his validation and love, cherishing the moment even as she is aware of her impending death.

Lee receives a second text from his dead roommate James’s phone, asking Lee to release him. Lee’s phone screen then cracks and the message disappears, making him question his perception. Panicked and experiencing Ativan withdrawal, he deduces that the opening to Sen’s world is governed by the ocean tides. He decides to find the spy’s body to prove his experiences with Sen are real. He digs in the forest where he believes the grave is but finds nothing, deepening his self-doubt.

He returns to the house and has a disturbing encounter with Jim, who suddenly no longer sees him and almost runs him over with his car. Later, Hina finds Lee while sharpening knives and says she knows he is keeping a secret. That night, Sen returns to Lee’s room, frantic. She demands Lee find her guns to fight the soldiers. When he says he can’t, Hina approaches, and a terrified Sen hides in Lee’s suitcase. Hina enters, holding a knife behind her back, but leaves after a tense exchange. Lee confronts Sen, who becomes distracted by a soy sauce stain on his shirt, triggering Lee’s own obsessive fixation with the stain. The moment leads to an unexpected intimacy, and Sen reaches into his chest, causing Lee to fall into a vision.

Lee is transported into a memory of the moments just before he killed his roommate, James. He is aware of what is about to happen, but is powerless to change it. James casually asks about his summer plans, mentioning he might travel to Asia and asking if Lee has ever been to Cambodia.

Sen is simultaneously thrown into a horrific vision of her own. She is back in a recent moment of her chopping wood, but when she swings the axe, she finds her brother Seijiro on the cutting block, the axe lodged in his throat. The yard is covered with the dismembered bodies of Sen’s mother and other brother, Kotaro. A vision of Lee’s mother, bruised and bleeding, appears and whispers something to her.

Sen shoves Lee away, breaking the connection and returning them to his room. Both are deeply shaken. Lee wants to re-enter the vision to learn more about his mother, but Sen lies, saying his mother said nothing.

Jim invites Sen to dinner. During the meal, Hina acts with open hostility toward Sen, questioning Lee’s fabricated backstory for her. The dinner is interrupted when Hina lunges at Sen with a kitchen knife. Sen, a skilled warrior, easily disarms her. Appalled, Jim orders Hina to leave the house. Hina pleads with Lee, insisting Sen is dangerous, but he sides with Sen, and Hina departs.

A flashback reveals Sen’s history with her father. Years earlier, when Itaro left to join the Satsuma Rebellion, she defied his orders and tried to follow him. Enraged, he brutally attacked her with his sword, called her weak, and abandoned her. He did not return until much later, after the rebellion had failed. His demeanor was so changed, behaving kind and supportive towards her, that Sen concluded the man who came back was an imposter.

Another flashback explores a traumatic memory from Lee’s 12th birthday. His mother made him a cake that tasted bitter, and after eating it, he became violently ill and was hospitalized for several days. His father downplayed the severity of his illness. When Lee returned home, he found his mother’s beloved flower garden had been completely dug up and destroyed.

After Hina leaves, Lee and Sen sit on the porch. He tries to initiate another spiritual connection, but touching no longer works. He experiences a mental health crisis, confessing his fear of being utterly alone. Sen comforts him and writes him a letter, making him promise not to read it until she is dead.

As Sen is about to leave, Lee reveals he knows how to prevent her death: She must leave her house and never return. Sen realizes he knows her fate. She demands to know if he can save her father, but Lee says only she can be saved. Furious, Sen accuses him of wanting her to live only so he won’t be alone. She declares she would rather die for her father than live for him, and disappears back into her world, blocking the door.

The day after Sen cuts him off, Lee finds the sea has ebbed away and the house is rapidly decaying. Sen’s door remains blocked. Hina’s car has reappeared, but she is nowhere to be found. Lee receives another text from James, urging him to dig. Lee throws his phone into the property’s well. In the kitchen, Jim makes the nonsensical claim that the police have called because Lee’s roommate has been found dead at the bottom of the well in their yard.

The story makes no sense, and Lee is overwhelmed. He sees the same mysterious stain from James’s shirt on his father’s shirt, triggering his rage. He grabs a knife to attack his father but instead stabs his own hand into the counter. As his father restrains him, police cars arrive; Lee realizes Jim set him up to be placed in a psychiatric hospital. Lee breaks free, runs to his room, and forces his way through the closet into Sen’s world, where he is immediately confronted by Sen’s father, who attacks him. Lee flees but is cornered in the yard, where Itaro raises his sword to deal a killing blow.

On the last day of her life, Sen dismisses the household servants to save them from the impending attack. Soon after, she finds her father about to kill a wounded Lee in the yard. She intervenes, but her father, enraged that she consorted with a foreigner, orders her to execute Lee herself. When she hesitates, he threatens to kill her, too. Seeing her impossible choice, Lee tells her he forgives her. His words grant her a moment of clarity. Sen understands at last that she is fated to become a ghost for betraying her only friend.

Freed from her obligation, Sen puts down her sword and defies her father, telling him that he is a coward. Just before Itaro kills her, the imperial army attacks. Itaro abandons Sen to join the fight. Sen helps Lee back to her room and pushes him through the closet door into his own time, sealing him out. Returning to the battle, she witnesses her brothers being shot and killed. Overcome with terror, she hides under the porch, feeling like a coward. As she weeps, something begins clawing up through the earth beneath her.

Trapped in his own time and bleeding badly, Lee crawls under the porch to die as police surround the house. A ghostly apparition of his mother appears, her face bruised and broken. She whispers a single word, “Dig,” and vanishes. Lee claws at the soft earth, which gives way to mud and then water, pulling him into a subterranean river.

Simultaneously, in her time, Sen also feels something beneath her and begins to dig, joining Lee in the water. As they float in the darkness between worlds, two small jeweled boxes with turtle carvings bob to the surface. They each take one and open it.

This chapter recounts the final part of the Japanese folktale of Urashima Tarō. Urashima Tarō returns from an underwater palace after what felt like only a few days, but when he returns to his village, he finds that 300 years have passed. His home is gone and his family is long dead. In his grief, he opens a forbidden jeweled box given to him by the sea princess. A cloud of smoke rushes out, carrying the stolen centuries. He instantly ages and turns to dust.