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.
Kampyo-maki (Gourd)
Kampyo are dried gourd strips from the gourd calabash. They are often used to balance out the fishy/ocean scent from seafood, but they're good on their own as well. Brown in color, the gourd has a sweet soy sauce-like flavor. Kampyo is thought to encourage digestion and is often ordered at the end of a meal.