Rinse the rice thoroughly, then add water and cook in a rice cooker until done. While the rice is cooking, mix the rice vinegar, sugar, and a pinch of salt until the sugar dissolves. When the rice is cooked, transfer it to a bowl and pour the vinegar mixture over it. Mix well, then cover with a towel and let cool. Prepare the crab meat, cucumber, and avocados by slicing them thinly. To roll the sushi, cover the bamboo mat with plastic wrap.

To assemble, cut a sheet of nori in half and place the shiny side down on the plastic wrap. Wash your hands before rolling, as gloves aren't recommended. Keep a bowl of cold water nearby to wet your fingers. Gently spread a thin, even layer of prepared rice over the nori. Sprinkle about 1/2 tablespoon of toasted sesame seeds over the rice and press lightly. Carefully flip the nori so the rice side is down on the bamboo mat. Arrange crab, avocado, and cucumber in a line, then roll up tightly, pressing gently to shape.

Serve with soy sauce, pickled ginger, and wasabi.