The court had ordered the death penalty for 13 people linked to the cult. Other members from bottom left to right, Yoshihiro Inoue, Tomomitsu Nimi, and Kiyohide Hayakawa. After that, the Tokyo detention center rejected requests for meetings with Asahara more than 400 times, citing the absence of a reaction from Asahara.
Kamikawa told a news conference that she had ordered the executions following "very careful consideration".
"The death penalty can never deliver this as it is the ultimate denial of human rights", Hiroka Shoji, the group's East Asia Researcher, said in a statement.
Kamikawa said that capital punishment is "unavoidable" for such heinous crimes.
One of the bases of the Aum Shinrikyo Doomsday cult.
Members of the Aum Shinrikyo cult left sarin, a deadly nerve agent, in plastic bags on subway cars and poked the bags with umbrellas before fleeing. The attack claimed the lives of thirteen people, over 6,300 people were injured.
A facility of Aum Shinrikyo doomsday cult led by its guru Shoko Asahara in Kamikuishiki in Kamikucishiki, Japan.
In this 2015 photo, Tokyo subway workers offered silent prayer 20 years after the poison gas attack.
Victims of AUM crimes and their families largely welcomed the move, which came decades after the crimes were committed due to prolonged trials.
Fusae Kobayashi, 76, who lost her son Yutaka in a 1994 sarin gas attack in the central Japan city of Matsumoto, said, "I have always thought executions will be carried out so my immediate reaction was 'finally'".
Shizue Takahashi, whose husband was a subway deputy station master who died in the attack, also expressed regret that six of Asahara's followers had been killed. "I think they would find it regrettable that they could not have heard the news of this execution".
Suga said authorities are taking precautionary measures in case of any retaliation by his followers.
And the execution of Asahara's followers risks elevating them to "martyrs" in the eyes of remaining cult adherents, warned Taro Takimoto, a lawyer for relatives of cultists, in an interview with AFP earlier this year.
Asahara had been on death row for masterminding a 1995 sarin gas attack on the Tokyo subways and other crimes.
Asahara, born as Chizuo Matsumoto, founded the group that became Aum Shinrikyo, or Supreme Truth, in 1984. In March 2006, the Tokyo High Court rejected his appeal without holding a public hearing because defense lawyers did not submit appeal documents by the deadline.
On 16 May, Shoko Asahara was finally arrested. Japan executed the leader and six followers.
The religion persists and has since split into the renamed Aleph and Hikari no Wa groups.
Virtually blind, he was seen as a charismatic speaker who cloaked himself in mysticism to draw recruits including doctors and scientists to the doomsday cult he developed in the 1980s.