Complications of stomach cancer did him in.
"Mr. Yamaguchi said he was less than 2 miles away from ground zero. His eardrums were ruptured and his upper torso was burned by the blast, which destroyed most of the city’s buildings and killed 80,000 people.
Mr. Yamaguchi spent the night in a Hiroshima bomb shelter and returned to his hometown of Nagasaki the following day, according to interviews he gave over the years. The second bomb, known as “Fat Man,” was dropped on Nagasaki on Aug. 9, killing 70,000 people there."