[1] The circumstances of his rise to prominence result from the fact that following the nuclear bombing of Hiroshima, many municipal employees were killed or incapacitated, while Hamai was only slightly injured.
Following Kihara's dismissal from his duties in March 1947 by the Allied occupation authorities and the reforms conducted in Japan by General McArthur, first mayoral elections were held in Hiroshima in April 1947.
In that election, Hamai ran against five other candidates, which included vice mayor Hisao Yamamoto and city council chairman Tsukasa Nitoguri.
As part of these efforts, he established a traditional annual speech delivered at the main memorial ceremony on August 6, known as Peace Declaration.
[4] To achieve that end, Hamai made numerous trips to the Japanese Diet in Tokyo along with his secretary Chimata Fujimoto and city council chairman Tsukasa Nitoguri.
[6] In addition, Hamai worked to establish ties with foreign peace activists, such as Norman Cousins, who first visited Hiroshima in 1949.
In June 1950 Hamai attended a conference in Caux, Switzerland, held by the Movement for Moral Re-Armament established by Frank N. D. Buchman.
[8] He opposed the establishment by the US Army of the Atomic Bomb Casualty Commission and tried to prevent the location of its facilities in Hijiyama park, but did not succeed in that.
[10] During the mayoral election of April 1955, Hamai's popularity was in decline as rumors spread he was under investigation for financial irregularities.
He put pressure on the government by holding a fund-raising campaign in the streets of Tokyo, which led to the donation of 60 million Yen to that cause.
[15][16] As a result, for the first time in human history, a World Constituent Assembly convened to draft and adopt the Constitution for the Federation of Earth.