[Danieru]

The coins, both the giving of and the expiring, are 100% a Japanese culture thing.

Most japanese residents can tell you near every store will have a points card system where you get 1% back in points. Or 0.5% for the stingy super markets.

What is lesser known is that by law such points, and even digital in-game currency, must expire else be considered money and regulated as such.