Since the red of the tuna’s flesh is supposed to look like steel being forged to make a samurai sword, tekka maki has always enjoyed something of a macho image in Japan. Typically, in restaurants, it’s the bits and pieces trimmed from tuna sashimi that are used in making these rolls. At home, you might want to practice your knife skills in making sashimi, keeping this recipe in mind as a fine way to use the less-than-glorious-looking slices that might resu