Prosecutors on Thursday sought the death penalty for a man charged over a 2019 arson attack on an anime studio that killed 36 people in Japan's deadliest crime in decades, reports said.

Shinji Aoba, who nearly died from burns he sustained, has admitted to starting the fire at Kyoto Animation and faces five charges including murder, attempted murder, and arson.

He is accused of breaking into the building in July 2019, spreading gasoline around the ground floor and setting it alight before reportedly shouting "drop dead".

Many of those killed in the blaze at the famous studio were young staff, including a 21-year-old woman, and more than 30 others were injured.

Prosecutors on Thursday requested the death penalty, saying Aoba "planned the incident based on a strong intent to kill and was well aware of the dangers of arson with gasoline," according to public broadcaster NHK. 

"Even when the victims fled, smoke followed them at excessive speed, and one can only imagine the sheer hellish terror and sorrow they must have felt," the prosecutors said.

The district court in the western city of Kyoto and prosecutors both declined to confirm the reports. A verdict is due on 25 January.

Support for executions

Japan is one of the few developed countries to retain the death penalty, and public support for capital punishment remains high despite international criticism.

The 45-year-old admitted starting the blaze when the trial began in September, and later said he "should pay for his crime" with capital punishment.

"I feel tremendously sorry and the feeling includes a sense of guilt," Aoba told the court on Wednesday, apologising for the first time, NHK reported.

"Please give me back my daughter," a mother who lost her 26-year-old told the court earlier this week, according to NHK.

"I wish I could go back to that day and die with her, at least by her side," she said.

Firefighters told reporters at the time that the incident was "unprecedented" and that rescuing people and extinguishing the fire was "extremely difficult". 

'Misplaced resentment'

Aoba was allegedly angry that his ideas had been stolen by the studio, known by its fans as KyoAni.

Prosecutors have told the court the arson attack was "committed out of misplaced resentment". 

Aoba had a "delusion" that the studio stole his ideas, they said, though Kyoto Animation denies this.

More than 90 percent of Aoba's skin was burned and a doctor who treated him told the Yomiuri newspaper that he required 12 operations.

Aoba regained consciousness weeks later and was said to have sobbed with relief after undergoing a procedure that restored his ability to speak.

The charges against him were made after a psychiatric evaluation.

His lawyers have entered a plea of not guilty, saying he "did not have the capacity to distinguish between good and bad and to stop committing the crime due to a mental disorder".

The blaze that ripped through the studio shocked Japan as well as the country's huge anime industry and its fans around the world.

Kyoto Animation is well known domestically and abroad for its role in producing popular TV anime series including "The Melancholy of Haruhi Suzumiya" and "K-ON!"