Kawai was an Imperial Japanese naval officer during World War II. In 1945, he was tasked with escorting the heart of Frankenstein's monster to Tokyo. Once at the laboratory in Hiroshima, Kawai was given a rare opportunity to see the heart, which was still beating this unnerved him a great deal. Thereafter he left Hiroshima and thus survived the stomic bomb blast that destroyed the city days later.
After the war, Kawai became the foreman at an oil rig. After Baragon destroyed his rig, Kawai caught a glimpse of the underground monster. When news reports of a vagrant boy who was resistant to radiation poisoning came from Hiroshima, Kawai became convinced that this boy had eaten the heart of Frankenstein's monster, or perhaps grown from the heart. This information he imparted to Dr. James Bowen and his colleagues.
Later, after Frankenstein escaped from Bowen's custody and began being blamed for all manner of death and destruction, Kawai remembered his brief encounter with Baragon at the oil rig. Convinced Baragon was responsible and not Frankenstein, Kawai sought to prove the mutant boy's innocence.