How many people know about the other 1964 Japanese 100 yen? Is it just another coin or something special?
Welcome to CT!! Nice coin. There were 10,000,000 minted in 1964 and is .600 silver. No to special or valuable imo. https://en.numista.com/catalogue/pieces9582.html
These are nice coins but also fairly common. You happen to have the year with the lowest mintage (昭和三十九年 or Showa 39 or 1964). The next lowest year is 1961 at 15,000,000. Yet all years before it have a slightly higher value. Perhaps people hoarded this particular year and plenty of nice examples exist? Hard to say. Still a nice coin. I'm not sure if that was your question, though. What do you mean by "the other 1964 100 Yen?" Commemoratives for the 1964 Olympics were minted that same year, but the 100 Yen doesn't have much value, either.
Actually I found the normal 100 yen a lot harder to find compared to the commemorative Tokyo Olympics 100 yen.