Tekka Don is a Japanese rice bowl that is topped with tuna sashimi. The sashimi is marinated in a mixture of savoury/sweet mixture of soy sauce, mirin, sake. The bowl also comprises garnishes of thinly sliced nori, chopped scallions, shisho leaves, sesame seeds etc. They look a lot like the Poke bowl served in Hawaii.  

The term 'Tekka' has a very interesting origin story. It is derived from 'tekkaba', or gambling rooms, where the dish was commonly served, especially during the end of Edo period(1603-1867) and the start of the Meiji period (1868-1912) in Japanese history. Around this time, the taboo around eating non-vegetarian food reduced, people were also more experimental with their palates and taste.  

This rice bowl recipe here is topped with tuna, sesame seeds, wasabi and roasted seaweed. And is made of many spices and ingredients.