Shōwa era 昭和時代
The reign of Emperor Shōwa, 1926–1989, spanning war, occupation and the economic boom; postwar Shōwa is when kinbaku took shape in magazines, photography, shows and film.
The Shōwa era lasted from December 25, 1926 to January 7, 1989, the reign of Emperor Shōwa (Hirohito), the longest of any Japanese emperor. The Heibonsha encyclopedia on Kotobank says no single image sums it up and divides it at the 1945 defeat: crisis, militarism and war before, then occupation, democratic reform and high economic growth after.
English Wikipedia credits the postwar magazine Kitan Club with popularizing bondage in the 1950s and has Osada Eikichi performing live SM shows from the 1960s. The historian Kawahara Azumi notes that the SM magazine boom began to fade in the mid-1980s as titles closed, around the time Nureki Chimuo’s Kinbiken gatherings began. More in SM magazines and pink film.