It's strange. First I thougth that it was worned out, but the others are very worn and still can be seen. Maybe somebody did it on intention, or it's a rare mistake.
The most expensive is a 1933 US $20 gold eagle. Here are others:
http://www.coinweek.com/featured-news/coin-rarities-related-topics-a-1907-10-gold-piece-becomes-the-latest-us-coin-to-be-auctioned-for-more-than-2-million/
It can be a very rare unaligned coin or a cheap. The biggest issue that I have is that it has almost no worn out parts, it reminds me of the old Chinese dollar copies. I'm not expert in Japanese coins though, it's what I think.