While a student, he belonged to the "Waseda Alumni Scenario Research Society" with Yōzō Tanaka and others, and produced documentary films.

In 1966, he formed Guru Hachirō (具流 八郎), a group of screenwriters led by Seijun Suzuki, together with Takeo Kimura, Yōzō Tanaka, Chūsei Sone, Yutaka Okada, Seiichirō Yamaguchi, and Yasuaki Hangai.

Yamatoya proceeded to direct such films as Inflatable Sex Doll of the Wastelands in 1967 and Not Much More Than a Pistol in 1968.

[1] He is best known as the screenwriter for Seijun Suzuki's 1967 film Branded to Kill,[2] which is "a stark, spastically existential—and, most affronting of all, defiantly unmarketable—crime-flick abstraction that unfolds like the director's cracked self-portrait.

"[3] Jasper Sharp, author of Behind the Pink Curtain: The Complete History of Japanese Sex Cinema, said, "Yamatoya is definitely very interesting.