The protagonist has to make a wish, and strongly suspects she’s dealing with a jackass wish-granter. So she wishes for a chocolate bar.
The wishing stone gives her a free coupon for a chocolate bar at the magical night market. There didn’t use to be a night market. Better hurry along now, though! She doesn’t want to know what will happen if she doesn’t go to the market and get the chocolate.
P.S. Holy crap, this game took a dark turn later on.