His lawyers had refused to submit the papers because they argued Asahara suffers from pathological mental stress caused by confinement and is unfit for trial.
Asahara, born Chizuo Matsumoto, was convicted in 2004 and sentenced to hang for the Tokyo attack and others that killed 27 people and injured thousands of others.
In the subway attack, cult members released lethal sarin nerve gas on trains converging in central Tokyo in March 1995. The fumes killed 12 people and sent thousands to the hospital.
The nearly blind former cult leader, who once commanded a powerful group of some 40,000 members, mumbled incoherently during his eight-year trial, interrupting sessions with bizarre outbursts in English.
But last month, a court-appointed psychiatrist submitted a report to the Tokyo High Court saying Asahara may be feigning mental illness and “had not lost the ability to stand trial.”
Lawyers could still appeal the High Court decision to Japan’s Supreme Court, but Asahara could hang if the top court sides with the earlier decision, NHK said.
About a dozen other cult leaders have been sentenced to death, although none of them have been hanged, and three cultists wanted in the subway gassing are still on the run.
The charismatic Asahara had predicted an apocalypse that only cult members would survive. The cult – which at its height claimed 40,000 members in Japan and Russia – was developing chemical, biological and conventional weapons in an apparent attempt to attack population centers and overthrow the government.