Elderly couple Mr. and Mrs. Tominaga find themselves hospitalized in the same ward of Heiwa Hospital, both diagnosed with cancer. She has stomach cancer while he battles lung cancer, and their adjoining rooms allow them to face treatment together. Their days are filled with quiet routines, small rebellions like smuggling flavor packets onto bland hospital food, and gentle banter about who might die first, inspired by a television program about octopuses where the male is easily caught alongside the female.

The Tominagas have two adult children. Their daughter Haruko visits with her own children out of a sense of obligation, her busy life creating a quiet generational disconnect. Their son Yuichi lives as a recluse in a dark apartment cluttered with trash, having retreated from the world after his father harshly dismissed his dream of becoming a manga artist, despite a one-shot publication. While the parents are confined to the hospital against their will, Yuichi remains confined indoors by his own choice.

A significant arc involves a foreign boy named Tom who is also hospitalized. Mr. Tominaga, a retired teacher, befriends the boy and decides to buy him a Spotch video game console, enlisting Yuichi's expertise for the purchase. This errand forces an awkward car ride where father and son begin to confront their past, particularly a childhood memory of the father driving across prefectures to replace a mistaken Santa gift. The arc ends tragically when Tom dies before opening the console, causing Mr. Tominaga to weep over outliving a child.

The narrative forces crisis when doctors inform Mr. Tominaga that his wife's cancer has spread to her liver, requiring her to be moved to a distant room. Their proximity has been their comfort, as they would playfully knock on the adjoining wall to reassure each other. As his wife declines, Mr. Tominaga's cancer spreads to his brain, causing erratic anger. Yuichi finally emerges from his room, pleads with hospital staff to reunite his parents, and sleeps disheveled in a nearby diner after ensuring their beds are pushed together.

In their final days, the couple returns to their traditional home. Mr. Tominaga tends his garden and harvests potatoes for his wife, but she appears to have passed by the time he returns to her side. Yet the end comes with them back in their hospital beds side by side. Mrs. Tominaga reminds her husband of the octopus program, concluding that as the male and female are caught together, they will die together. The family drama resolves as Yuichi performs one final act of service and the father realizes his criticisms stole his son's motivation, bringing a measure of reconciliation before the conclusion.