A Japanese man sentenced to death for an arson attack that killed 36 people at an anime studio appealed the ruling on Friday, a court said.

Shinji Aoba, 45, was convicted on Thursday over the 2019 blaze at the studio of Kyoto Animation — Japan's deadliest crime in decades.

His lawyers had entered a plea of not guilty, saying he had a mental disorder, but the judge rejected this.

On Friday, his defense team filed an appeal against the ruling, a Kyoto District Court spokesman said.

Japan is one of the few developed countries with capital punishment and public support for it is high. As of December, 107 people were on death row.

Many of those killed in the July 2019 fire were young, including a 21-year-old woman.

On the day of the attack, Aoba broke into the building in the morning, splashed gasoline around the ground floor, lit it and shouted "drop dead," survivors said.

The victims "were engulfed in fire and smoke in the blink of an eye ... They died an anguishing death as the studio instantly turned into a hell," presiding Judge Keisuke Masuda said in his ruling.

"Immolating people is truly cruel and inhumane," the judge added.

Aoba himself sustained burns on 90% of his body and only regained consciousness weeks after the fire, and the ability to speak later still.

Aoba believed that the studio — known among fans as KyoAni — stole his ideas, prosecutors said, a claim the company has denied.

A number of victims were found on a spiral stairwell leading to the roof, suggesting they were overcome as they desperately tried to escape. More than 30 others were injured.

Firefighters called the incident "unprecedented," saying that rescuing people trapped inside was "extremely difficult."