The players owed their lives to the fact that the local police had ordered the game moved from the center of Hiroshima.
A three-game playoff was held in 1946, with Iwamoto winning two straight games to take the Honinbo title.
Iwamoto defended the Honinbo title against Kitani Minoru in 1947, and in 1948 achieved 8-dan, becoming president of the Nihon Ki-in.
In his later years he was the main benefactor to several European and American Go centers in London, São Paulo, New York, Seattle and Amsterdam, largely through setting up the Iwamoto Foundation in 1986, with an initial contribution of 530 million yen.
In 2014, the Nihon Ki-in and the American Go Association jointly founded the Iwamoto North America Foundation for Go, in order to "foster, promulgate, and develop the game and culture of Go in North America according to the vision and wishes of the late Japanese Go master, Iwamoto Kaoru.