Whats the sauce that chefs put on the sushi pieces?

I really love the seasoning that they use on their seared fishes. It tastes savory and like almost sesame ish, but when i use sesame oil at home it doesnt taste good like the ones in restaurant. the one that kura sushi uses on their umami oil seared beef is what im thinking of. I brought home some seared salmon from work and it had this great flavor to it, savory and delicious and im dying to know what it is. I would ask the chefs but they scare me and get very grumpy when i ask them anything😔