The difference between Japanese BBQ sauce and regular BBQ sauce is Japanese BBQ sauce has a complex, umami rich, sweet and savory flavor profile that is built on a base of mirin and soy sauce with additions of ingredients like green onion, garlic and ginger.
Regular BBQ sauce or American BBQ sauce is made with a tomato paste or ketchup base and offers a sweeter, tangier and often sometimes a spicier taste that comes from ingredients like spices, vinegar, molasses and brown sugar.
American or regular BBQ sauce is often thicker and richer than Japanese BBQ sauce as well.
And Japanese BBQ sauce is often thinner and free of any thickeners, which makes Japanese BBQ sauce great for dipping, grilling and marinating.
In Japan Japanese BBQ sauce is more for marinating or dipping cooked meat into, versus basting in the American tradition of American BBQ sauce.
Basically what makes Japanese BBQ sauce different from American BBQ sauce is the rich umami flavor profile, more balanced sweet and savory taste and a lighter and often thinner consistency.
Japanese BBQ sauce is rooted in traditional tare sauce that is used for glazing and dipping and commonly includes soy sauce, mirin, sweet rice wine, sugar and fresh aromatic ingredients like ginger, garlic and sometimes a miso paste, which creates a tangy, umami rich and fresh taste.