A 24-year-old man dressed as the Joker character from the Batman comics attacked passengers on a Tokyo train line on Sunday evening.
As many as 17 people were injured as they headed for Halloween parties in the city.
Witnesses say the suspect sprayed a clear liquid around the carriage and set it alight.
Video footage showed passengers running through carriages away from flames and clambering out of train windows, reports the BBC.
"I thought it was a Halloween stunt," one witness told the Yomiuri newspaper about the attack. "Then, I saw a man walking this way, slowly waving a long knife."
The attack happened at around 20:00 local time (11:00 GMT) near Kokuryo station, in the city's western suburbs. Eyewitnesses said the suspect was wearing a bright purple and green suit.
Media reports say the man was arrested by police on the spot.
According to news outlet Kyodo, he told police he adored the character Joker in the Batman comics.
The Joker is a super villain in the comics and batman's archenemy. In fact, the 2019 hit movie Joker starring actor Joaquin Phoenix featured a violent scene where he attacks several men on a train after being repeatedly harassed by them. It's a pivotal scene, marking the beginning of the character's transformation into the Joker.
Local media reports say that the suspect told authorities he wanted to kill people so he could be sentenced to death.
The AP news agency, citing the Tokyo Fire Department, said three of the injured had serious wounds. Local media reports an elderly man was unconscious after being stabbed in the attack.
Video from the scene shows passengers running from the attacker, stumbling through a connecting door between carriages and climbing through the train's windows after it made an emergency stop.
Shunsuke Kimura, who filmed one of the videos, told the national NHK broadcaster that the scene was "horrifying". "Train doors were closed and we had no idea what was happening, and we jumped from the windows," he said.
Violent crime is rare in Japan but there have been a number of high-profile knife attacks in recent years.
Ten people were injured by a knife-wielding man on another Tokyo commuter train in August. In 2019, a man attacked a group of schoolchildren waiting for a bus in Kawasaki, killing two and injuring at least 18 others.
