Japanese police on Wednesday formally arrested a man on suspicion of an arson attack on an animation studio in Kyoto last year that killed 36 people, a police spokesman said.

The horrifying attack on the well-known Kyoto Animation anime studio was the deadliest violent crime in decades in famously safe Japan, and shocked the country.

Shinki Aoba allegedly broke into the building, "scattered gasoline on the ground floor, set fire to it," and killed 14 men and 22 women, a police spokesman said, confirming his arrest on suspicion of murder Wednesday.

Aoba, 42, was detained in the immediate aftermath of the July 2019 attack, which also injured dozens of people. But he was hospitalised immediately, suffering serious burns.

He was reportedly unconscious for weeks and police held off charging him until his condition stabilised.

No motive for the attack has been established, with reports claiming Aoba shouted "drop dead" before the assault.

He has reportedly confessed to the arson, and there have been claims that he accused the studio of stealing his work.

In addition to the charge of murdering the 36 people who died in the attack, Aoba faces attempted murder charges over the 34 people who suffered injuries. He is also charged with possessing knives on the street without legitimate reasons, in violation of Japan's strict laws on weapons.

Aoba is still recovering from his burns, but police have prepared medical treatment facilities at a police station to which he will be sent, public broadcaster NHK reported.

Many of those killed in the blaze were young, including a 21-year-old woman.

The devastating attack on Kyoto Animation was one of the deadliest violent crimes in decades in famously safe Japan
The devastating attack on Kyoto Animation was one of the deadliest violent crimes in decades in famously safe Japan AFP / Buddhika Weerasinghe

Parents of some of the victims told local media they were still suffering the devastating loss of their loved ones.

"I think about her very often," Shinichi Tsuda, whose daughter Sachie was killed in the fire, told NHK.

"I think about her at the time of the incident, wondering how painful it would have been for her."

Yasuo Takemoto, who lost his son Yasuhiro, a director at the studio, said the 10 months since the attack had "passed quickly."

"But it doesn't mean that we are cured 10 months later. Yasuhiro won't come back," he told NHK.

The attack sent shockwaves through the anime industry and its fans in Japan and around the world.

"These are people who carry the Japanese animation industry on their shoulders," Kyoto Animation's president Hideaki Hatta told reporters at the time.

"It's heartbreaking. Japanese jewels were lost."

Kyoto Animation, known by its fans as KyoAni, is well-known both domestically and internationally 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 Japanese city of Kyoto.

Its work often featured elaborate screenshots described as "KyoAni quality" by enthusiastic fans.