A game

These two young ladies are offering a game of some sort. The sign, written on part of a cardboard box, says, 'Water Coin'. I did not go over to see what it was but I suspect that you could win some sort of small prize by dropping a coin (100 yen, about US$1.00) into the plastic box. If you were accurate enough to hit the right spot the prize would appear. At least that is what I think it might have been.