Coupons are the basic unit of currency in The Tomorrow Children. They are awarded to players by the Labor Ministry in exchange for their toil. High-value toil (like killing monsters) receives more coupons. Coupons can be used to purchase items at all of the official government shops, e.g., the Union Market, the Electrical Market, the Military Market, and so on.
Coupons cannot be used to purchase items from the Black Market.