Kodaira killed his father-in-law in 1932 and later raped and murdered at least 7 women between 1945 and 1946 by inviting them into forested areas around Tochigi and Tokyo under the guise of giving them food or employment.

Reportedly, Kodaira raped many women in China and, in one instance at the Taku Forts, stuck a sword into the belly of a pregnant woman.

Kodaira was living in Tokyo at the time of the Surrender of Japan in August 1945, and used the post-war situation to exploit vulnerable women for his benefit.

On 12 July, Kodaira invited a 22-year-old woman at Shibuya Station into the woods to work for a farmer, but then murdered her and stole her money.

On 15 July, Kodaira invited a 21-year-old woman at Ikebukuro Station to a farmhouse in the woods where she was raped and strangled to death before stealing her money and geta.

On 28 September, Kodaira invited a 21-year-old woman at Tokyo Station to the woods where he raped and strangled her to death before stealing her money and clothes.