The fire department received the alarm at 10:18 a.m. and had the blaze nearly extinguished by 10:46. In those twenty-eight minutes, the fire itself remained contained to a relatively small area on the fourth floor. The building's exterior showed little damage. But inside the clinic, the physics of combustion were lethal. Gasoline ignited at the reception area sent flames racing across the floor, blocking the only path to the building's emergency stairs and elevators, which were located outside the clinic's entrance. Two survivors near the reception desk managed to escape. The remaining patients and staff, cut off from the exit, retreated into the clinic's inner rooms -- treatment spaces with no windows and no alternative escape route. Smoke and carbon monoxide filled those sealed rooms in minutes. A doctor who later treated casualties confirmed that most victims showed minimal external burns. They had not died from flame. They had suffocated.

The attacker was Morio Tanimoto, a 61-year-old Osaka resident who had been a patient at the clinic for two to three years. Investigators found that Tanimoto had purchased 10 liters of gasoline in November 2021. Following regulations enacted after the 2019 Kyoto Animation arson attack, gasoline buyers in Japan must present identification and explain the purchase's purpose. Tanimoto showed his ID and told the seller the fuel was for his motorcycle. Police discovered a newspaper clipping about the Kyoto Animation attack in Tanimoto's home, leading investigators to characterize the Osaka fire as a possible copycat. Tanimoto had a history of violence: in 2011, he had stabbed his own son in the head and served prison time for the act. On the morning of the attack, he carried a knife in addition to the gasoline, and witnesses reported he deliberately blocked a person attempting to reach the elevator. Tanimoto sustained severe burns in the fire he started and died on December 30, 2021, without ever being formally charged.

The tragedy exposed a fundamental vulnerability in Japanese building design. The Dojima Kita Building had a single stairwell -- common in commercial buildings constructed under older codes -- and the clinic's interior layout funneled all foot traffic through one entrance. When that entrance became a wall of fire, there was no alternative path to safety. Prime Minister Fumio Kishida called the attack a tragic incident and pledged to investigate its causes. Osaka Governor Hirofumi Yoshimura confirmed that police were treating the fire as arson. The most consequential response came from Minister for Internal Affairs and Communications Yasushi Kaneko, who ordered inspections of approximately 30,000 buildings across Japan that have three or more floors but only a single stairwell. The order was an acknowledgment that the Dojima Kita Building was not unusual. Thousands of commercial buildings shared the same design flaw -- a layout where one blocked corridor could turn an entire floor into a sealed chamber.

What makes the Osaka building fire especially painful is the nature of the target. This was not an office building or a commercial space. It was a clinic where people came at their most vulnerable -- seeking treatment for depression, anxiety, and other conditions that carry significant stigma in Japan. The victims, fourteen men and ten women ranging in age from their twenties to their sixties, were patients and staff. They were people who had taken the difficult step of asking for help. In the aftermath, mental health advocates in Japan spoke about the attack's chilling effect: the fear that people who already struggled to seek psychiatric care might now avoid clinics altogether. Memorials placed near the site in the weeks that followed reflected the community's grief for a place that had been, by every account, trying to do good work in a society that often leaves mental health struggles unspoken.