Although there are souvenior shops in every tourist destinations in Europe, the products sold at the souvenior shops are totally different in Japan. Then, souvenior shops are different too.
If you hear souvenior, you will imagine key ring, magnet, coffee mug or T-shirt of the place where you visit. However, souvenior in Japan is food rather than these items which you cannot eat. There is a custom in Japan to buy a local food which you have visited and bring it back to home. Then, mostly Japanese do not buy just one of it but will buy several items due to bring the local food, especially confection to their offices and offer to their colleagues. If you want to buy the local confection in Europe, you probably must go to the local supermarket to buy it. On the other hand, supermarkets in Japan usually do not sell these local confection at all.
It is almost same concept as duty free shops at the airports but you can see these shops outside of airports at large stations or near the tourists attractions, such as major temples and shrines. Sometimes these local shops only accept cash, therefore recommend to carry some cash with you.