Tekkamaki (tuna sushi roll) (鉄火巻)
Usually, wasabi paste is also rubbed into it, thus people just dip it in soy sauce and eat it. There are many explanations regarding the origin of the name, Tekkamaki, such that tuna's red flesh resembles red-hot iron, or it came to be called "tekka" (iron fire) because, in those days, it was not the custom to eat raw tuna so using tuna flesh as an ingredient was a ridiculous thing (just like to touch hot iron), or, in old days, sushi was a kind of fast food which people could eat them while enjoying gambling at a tekkaba (gambling room). This tekkamaki is an Edomae-zushi (hand-rolled sushi) which uses tuna but is wrapped with a sheet of dried seaweed, so people can eat it without using chopsticks or getting their hands dirty. This shares a common origin with the one for sandwich of the West.
The dish that consists of vinegared rice with slices of red flesh of tuna on top in a china bowl is called "Tekka-don" (Tuna Rice Bowl).