When you mention "sushi" vegetarian and vegan options may not be the first ones to come to mind, but they are common and offer a refreshing dining experience.
Trying sushi is a major attraction for visitors to Japan, and there are many vegetarian and vegan sushi options for those with dietary restrictions. Try them in nigiri (hand-pressed) sushi, te sushi (a single hand-rolled style) or in maki (rolled, usually sliced) sushi
It should be noted that some of the vegetables or toppings may have been marinated with a fish-type broth (for example: bonito) as opposed to a konbu (seaweed) based broth, so check with the restaurant beforehand.