Of course, in established Japanese kitchens an array of knives would be available, each performing a particular function. Rest assured, if you wish to dabble, preparing sushi in your less than Nobu-esque style kitchen. I assure you, this is not the case.
A sushi knife should do everything; from slicing vegetables to the final cut of the sushi roll. Generally a good strong, sharp kitchen knife should do the trick- for the sake of your fingers, the sharper the better!
If you do however wish to purchase a “special” knife, simple all purpose sushi knives are available to purchase on the web and in most good department stores for around £35. A sushi knife must be made from strong material, high-end stainless steel being a popular choice. Handles ought to be functional, comfortable and durable. Beginners may, at first find it difficult to use a genuine sushi knife, as only one edge is typically sharpened, the Katoba, in order to cut with refined precision.