Kimura considered the screenplay for Ishirō Honda's Matango to be his best work, and he considered all of his scripts from Frankenstein vs. Baragon onward to be merely work for hire. To express this dismissive view of his later work, he started writing under the pseudonym "Kaoru Mabuchi". He chose the name "Kaoru" to project an image of anonymity because it can be either a male or female name.
Kimura was known for having a dark and gloomy personality, and he was reportedly never very close to any of his fellow Toho employees. He died from a throat obstruction in his Tokyo apartment in 1988.