Roll sushi (hosomaki) with raw tuna (maguro) and wasabi. 鉄火巻。
The name "tekka" is interesting. According to some this refers to the color of the sushi, which is like "red hot iron." More probable is the explanation that in the Edo-period these sushi were a favorite food in "tekkaba," gambling joints, because one could eat without making the hands dirty and even play on during the meal.
Tekkamaki are eaten with a soy sauce dip. The Tekkamaki in the picture below are thicker than the normal hosomaki as they contain extra tuna ("gudakusan," "with extra ingredients"). Also, they are from a supermarket and not a traditional sushi shop - the sushi shop would have the tuna exactly in the middle of the roll.
[Tekkamaki. Photo Ad Blankestijn]