In April 1959 Hamai was reelected as mayor and served in that position until 1967. During this term, he had the opportunity to establish the first sister-city relations with another city, which was the city of Honolulu, Hawaii. These relations were established due to the large percentage of Hiroshima immigrants in Hawaii. In late 1966 and early 1967 he was at odds with the Japanese government over the preservation of the Atomic Bomb Dome, which the government in Tokyo refused to finance. 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.