Tokyo Sonata tells the poignant story of the Sasaki family, consisting of Ryūhei, his wife Megumi, a dedicated housewife, and their two sons, the late-teen Takashi and the middle-schooler Kenji. Within their household, emotional connections are scarce, and genuine communication is a rare occurrence.
After losing his stable office job due to his company’s decision to hire cheaper labor from China, Ryūhei finds himself in a state of growing desperation as he struggles to secure new employment. He reconnects with an old classmate, Kurosu, who has faced a similar fate. Both men conceal the harsh truths of their circumstances from their families, bonding over shared woes. However, tragedy strikes when Ryūhei discovers that Kurosu and his wife have tragically taken their own lives, presumably due to Kurosu’s overwhelming despair.
Meanwhile, driven by noble intentions, Takashi decides to enlist in the United States military, a choice that deeply angers Ryūhei and saddens Megumi. On the other hand, Kenji grapples with guilt after inadvertently causing his classmates to insult their teacher. Eager to learn the piano despite his father’s adamant disapproval, Kenji secretly starts taking lessons from a kind-hearted teacher, Miss Kaneko, using his lunch money to pay for them and practicing on a damaged keyboard he salvaged from the trash. As he hones his skills, he and Miss Kaneko grow close, with her recognizing his exceptional talent and encouraging him to follow his musical dreams. When his parents uncover his secret lessons, a furious Ryūhei lashes out in anger, physically hurting Kenji and sending him tumbling down the stairs, leading to a minor concussion.
In a bizarre turn of events, Megumi, who feels increasingly isolated and worries about Takashi, becomes a hostage to a desperate burglar in their own home. The robber forces her to drive a car he has stolen, but during a stop at a mall, she has a moment to escape. However, upon unexpectedly encountering a distraught Ryūhei, now working as a low-paid janitor, she chooses to return to her captor, and they slowly develop a connection as they continue to journey without a clear destination.
That evening, all three family members confront their personal crises away from home. Kenji, after trying to assist a friend fleeing from an abusive father, is caught by the police and held in an adult cell overnight but is soon released. Megumi continues her travels with the burglar, spending the night in a shed by the sea. Despite the robber’s initial advances, he is unable to proceed, and they find solace in each other’s company. However, when Megumi sees a distant light on the horizon, the robber’s despair deepens as he cannot perceive the hope it represents. The next day, the robber drives the stolen vehicle into the ocean, leading Megumi back home.
Simultaneously, Ryūhei stumbles upon a stash of cash at his janitorial job but is then struck by a speeding vehicle, left unconscious but waking up surprisingly intact to abandon the money the following day.
Eventually, Kenji, Megumi, and Ryūhei find themselves back together at home, engaging in a mundane meal that lacks any acknowledgment of their individual journeys. Four months later sees the family adjusting to the new status quo—Ryūhei continuing his janitorial role, Takashi opting to remain in the Middle East despite Japan's withdrawal orders. The film culminates with Kenji flawlessly performing Claude Debussy's "Clair de Lune" at an audition, evoking tears from his parents as the entranced audience watches their family share this tender moment together.
