A Japanese man reportedly angry that his ideas had been stolen admitted Tuesday to starting a fire that killed 36 people in an animation studio in 2019, local media said.

The blaze that ripped through the studios of Kyoto Animation in July 2019 shocked the anime industry and its fans in Japan and around the world.

"It's correct I've done" what is in the charges, Shinji Aoba said at the Kyoto District Court, according to the Jiji Press news agency.

"I didn't think so many people would die and now I think I went too far," said the 45-year-old who appeared in a wheelchair.

Aoba's lawyers however pleaded not guilty, citing mental incompetence, the reports said.

Aoba, who nearly died from burns he himself sustained, faces five charges including murder, attempted murder, and arson, according to local prosecutors.

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

Many of those killed in the blaze were young staff, including a 21-year-old woman. More than 30 others were injured.

Firefighters told reporters at the time that the incident was "unprecedented" and the mission to rescue victims and extinguish the fire was "extremely difficult".

Aoba's motives were unclear but there have been claims that he accused the studio of stealing his work, which Kyoto Animation has denied.

Its president Hideaki Hatta said he was "heartbroken for the employees who lost their lives and people who were close to them" ahead of the hearing, according to public broadcaster NHK.

The charges were made after a psychiatric evaluation, local media said.

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

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

The doctor, Takahiro Ueda, said he was not allowed by police to talk about the incident, but he told Aoba that "taking someone's life is not acceptable for any reason".

"I want him to explain everything at the court, and express sincere regret and apologize" to the victims and their families, the doctor said on Sunday.

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

While many animation studios are based in Tokyo, the firm reportedly felt strongly about remaining in the ancient western city of Kyoto.