In Japan some people make a sushi cake just for fun. I have never seen sushi cakes in any restaurants though.
It’s actually easy to make because making hand-rolled sushi and making sushi rolls are not necessary. Same ingredients for making sushi are needed, but also a cake pan is needed. All you we do it that put rice, ingredients in a middle layer (if we want), put another layer of rice, and decollate with ingredients. Instead of frosting, people usually use cream cheese.
It’s so easy and fun! If you are interested, please try!