As part of his efforts to rebuild Hiroshima as a city of peace, he used the services of architect Kenzo Tange to build a monument to the victims in Hijiyama park, now officially named peace park. One venue of action taken by him was receiving monetary contributions for the reconstruction of his city. One such major source has been residents of Hawaii, especially of Japanese origin. 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. Despite being a hibakusha himself, Hamai did express in early 1955 some support for the notion of establishing nuclear power plants in Hiroshima.