Yao Deer Motor Atsugi Factory, 1952?
I very much doubt this machine was the inspiration for Stallone's series of films, but this is another one that is a bit of a puzzle as the Japanese Wikipedia listing shows two companies making a Rocky (ロッキー号) motorcycle. The Yao Deer Motor as listed in the photo, made a four stroke, 150cc version in 1952 and as well a Rocky was made by a company called Shima Engine Industry (嶋エンジン工業所). Whether that is just a name change, a Wikipedia error, or two completely different manufacturers is unknown at this point (at least by me). In the text, it does show it as a 'B' version which would imply that an earlier one existed, so I've included both company names in the Compendium for the moment. The photo is from the Japanese History of Motorcycles, page 144 and shows the Yao Deer Motor version.