Prepare the rice according to the directions on the package. Once cooked, set rice aside in a mixing bowl and season with salt and rice wine vinegar to taste. Allow rice to cool to room temperature.
Make the miso soup: Place the miso into a small bowl, add a little hot water, and whisk until smooth. (This will ensure it doesn’t clump.) Place the miso, broth, scallions, and tofu in a medium saucepan and bring to a low simmer. Once done, stir in the nori and keep covered with a lid to keep warm. Reheat if needed before serving.
Place a nori sheet on a bamboo mat (or use a piece of plastic wrap on top of a towel).
Spread the rice evenly on the nori in the center of the nori covering as much of it as possible. (Leave about 1 inch along the top and bottom of the sheet uncovered, as this will be how you seal your roll. Make sure the rice is warm but not hot. If rice is too hot, nori will likely tear.)
Lay the crab, cucumber, and avocado across the middle. Start to roll the nori over the filling and gently press along the length of the roll. This motion presses the rice and the filling together and prevents the roll from being too loose. Continue to roll the sushi until you've rolled past the far edge of the nori sheet.
Once rolled, gently press and form the length of the roll to make sure it's compact and tight.
Slice the sushi roll into 6-8 pieces (you may have to rinse or wipe the blade in between slices to prevent sticking and tearing).
Garnish with sesame seeds. Serve with wasabi, pickled ginger, and soy sauce.
Serve the sushi with miso soup and Sapporo.