In contemporary Japan, the Suzuki family, consisting of the office worker Yoshiyuki Suzuki, his wife Mitsue Suzuki, and their two high school children, Kenji Suzuki and Yui Suzuki, navigate life in a suburban apartment complex in Tokyo. Unfortunately, their relationships are strained as each member prioritizes their individual pursuits, leading to a disconnect within the family dynamic. Suddenly, the city is plunged into a total blackout, causing all man-made systems to fail, and leaving the residents in chaos.
Faced with the consequences of this blackout, Yoshiyuki's superior informs him that his job is no more and advises him to escape to the countryside until the electricity is restored. This decision prompts the Suzuki family to travel to their ancestral home in Kagoshima, where Mitsue's father resides. Initially considering a flight from Haneda Airport, they ultimately opt for a more arduous bicycle journey, as it is one of the few viable transportation methods during this crisis.
During their trip, the family stops at a rest area where they encounter a fellow traveler who asks for water. However, Yoshiyuki, aiming to conserve their limited supplies, falsely claims they only possess one bottle left. That night, disaster strikes when a thief stealthily takes one of their remaining bottles of water. In a moment of compassion, Kenji chases after the thief, only to discover he is a desperate man struggling to provide for his wife and newborn child. This revelation leads Kenji to abandon his pursuit, opting for empathy over vengeance.
As they journey on, the family finds themselves navigating through a dark highway tunnel. They meet a group of blind elderly women who offer to guide them safely through the tunnel in return for food supplies. Eventually, their water runs dry as they take shelter from an incoming typhoon under a bridge. Unfortunately, Yoshiyuki suffers from severe diarrhea after drinking contaminated river water, and a storm washes away their clothing and the remaining supplies. With their situation becoming increasingly desperate, the family resorts to eating pet food and battery water. Despite damaging his bike, Kenji ingeniously fixes it using a part of his phone case.
Along their way, they encounter the Saito family, who have managed to survive on dried provisions and wild plants. After a brief interaction, both families part ways as the Saito family decides to head toward Nagoya. While passing through Osaka, the Suzukis arrive at an aquarium where a food distribution is taking place, but are disheartened to discover that all supplies have been depleted. In a moment of desperation, Yoshiyuki kills a pig found in a nearby field. A local resident named Zennichi Tanaka assists them by preparing the pig’s organs, and in return, the Suzukis help him with chores for some much-needed smoked meat.
After a week of recovery and nourishment, the Suzuki family, now better equipped, continues on their journey. However, they soon face another obstacle: a river without a bridge to cross. Resourcefully, they construct a makeshift raft, but their efforts are thwarted by a sudden rainstorm, leading to a disastrous outcome where Yoshiyuki and the bikes are swept away by the strong current, presumed dead by his family.
Undeterred, Mitsue, Kenji, and Yui continue on foot along the railroad tracks until they are attacked by a pack of dogs, drawn by the scent of their smoked meat. Fortunately, a train whistle scares the dogs away, and they are rescued by passengers onboard, where a doctor tends to Mitsue's fractured ankle.
In a twist of fate, Yoshiyuki is discovered alive, finding himself in an empty rice field. Spotting the train, he signals for help with a flare just in time to reunite with his family. As they finally arrive in Kagoshima, the emotional reunion takes place between Mitsue and her grandfather, marking a significant milestone in their journey.
Fast forward two and a half years post-blackout, Yoshiyuki awakens one morning to the familiar sounds of an alarm clock and music resonating throughout the town. The family watches in mixed emotions of joy and astonishment as the power is finally restored. Upon their return to Tokyo, the news reveals that the blackout was caused by a solar flare, a phenomenon still under scrutiny. The film concludes with the family receiving a photograph from the Saito family, showcasing a moment from their shared journey on the highway, embodying the connections formed during their trials and tribulations.
