This is a ¥500 coin, the largest value coin in Japan. Not too long ago it was worth roughly $5, but now with the rapidly declining yen, it is only worth about $3.33. Even if we stick to the yen, inflation has made it much less useful than it once was. Time was when we could find a lot of sales or deals based around this ¥500 coin. They'd call themselves one coin deals or something like that, using "one coin" to refer to the fact that just single coin has a relatively large buying power. Unfortunately these kinds of sales have grown less over the years as inflation makes ¥500 less valuable than it once was.