Shumai originated from Chinese-style dumplings,  but changed to match Japanese taste just like Gyoza.  Shumai are steamed pork fillings stuffed in Shumai wrappers. They are eaten alone or dipped in vinegar soy sauce with mustard.  In the US, you can find Chinese shumai at Dim Sum in Chinese restaurants for breakfast/lunch.  They can be wonderful in your lunch box and also as a tasty main dish for dinner.