Maeyama was born in the village of Sanwa, Nakakubiki District, in the city of Takada (now Jōetsu), in the Niigata Prefecture,[2][4] which is on the coast of the Sea of Japan.
During GUN’s initial few years, Maeyama was known for making artwork featuring mirrors and female iconography in a pop art manner, such as in Breaching an Idea (1967).
The experience laid the groundwork for GUN’s Postal Mailing Front, which sought to forge a nationwide antiwar alliance among teachers and activists.
Their methods included physically altering the postcards, affixing no or insufficient postage, inscribing a bogus sender and/or recipient, and creating other forms of confusion.
[14] Maeyama subsequently incorporated the returned postcard and official notice into his March 1970 contribution to the publication Psychophysiology Research Institute.
According to art historian Reiko Tomii, Maeyama's intervention challenged the postal system as a state-run institution, especially within the conformity of Japanese society.
The inaugural issue in March of 1971 proclaimed “Stand Up, All Fighting Workers, Students, and Citizens, for the Anti-Imperialism Struggle!”[15] As part of the newsletter, Maeyama designed three stickers with the words 反保 (Anti-Anpo), 反戦 (Anti-War), and 叛軍 (Anti-Military).
[15] In a similar vein, Maeyama also created “Antiwar Flags“ that year featuring three banners displaying 反軍 (Anti-Military), 反帝 (Anti-Imperialism), and 反戦 (Anti-War).
In May of 1971, Maeyama was invited by the critic Ichirō Haryū to show his “Antiwar“ ensemble of stickers and flags at Mainichi Contemporary at the Tokyo Metropolitan Art Museum.
Maeyama withdrew his work within a week of opening, however, in response to the event organizer’s removal of his donation box for those interested in obtaining the Antiwar Stickers.
However, as a follow-up to their earlier political art, in 1977, one year after the 50th anniversary of Hirohito's reign (r. 1926–1989), GUN created work to mark the occasion.