the competition for sumo would most likely be Fuji sushi and Kabuki sushi.
Fuji is the main competition because it is right down the street from Sumo and is relatively the same. I have long heard of the rivalry between people at OC's preferences. Many prefer Sumo (me included) and many prefer Fuji (idiots).
Kabuki is brand new and more upscale and because of that more expensive. I don't know if that makes it a part of the competition because the price ranges are so different but Kabuki is just donwn the street from Sumo and Fuji.