Although I know little of Akio Jissoji’s other works than the tokusatsu shows he directed, it seems that his activities with the ATG as a film director has been described as the integral part of his film works after he resigned TBS in 1970 to become an independent film director.
The ATG (Nihon=Japan Art Theater Guild) was likely to have been known as a Japanese movie company that existed from 1961 to the 1980s producing and distributing artistic movies of good qualities with non-commercialism policies as it had an enormous influence on the Japanese movie industry even though I knew little about it unfortunately.
While chances are Jissoji was also noted for the indecent depictions featured in his movies. Moreover, Jissoji is said to have described the highlight of the Tsuburaya tokusatsu as the fetishism shown in their tenacity towards even textures of the objects including the miniatures, allegedly adding that he hated to see a computer-generated Godzilla rampaging in the city (I think he had said that before a computer-generated Godzilla was actually realized).
In addition, Jissoji seems to have been a fan of the anime “Evangelion” and, also, to have liked anime-like girl figures openly stating he was a big collector of them.
After Jissoji was involved in the show “Kaiki Daisakusen (Operation Mystery)” aired from 1968 to 1969 with the Tsuburaya Productions, he resigned TBS in 1970, as I mentioned above, and formed a company named “Kodai Group” with Noriyoshi Ikeya, kaiju designer for Ultraseven after Tohl Narita, who left the Tsuburaya Productions.
As some staff who left the Tsuburaya Productions founded their own company called “Nihon Gendai Kikaku (Japan Modern Planning),” Jissoji and Ikeya are likely to have named their company Kodai (meaning ancient) wittily contrary to the Gendai.
The tokusatsu show created by the combination between the Kodai Group and Nihon Gendai Kikaku was “Silver Kamen” (1971-1972).