For onigiri with red cabbage and smoked tofu, first chop the smoked tofu and red cabbage very finely and mix with a little salt in a bowl.
Rinse the rice under running water in a colander until the water runs clear. Pour 600 ml of water into a pot, add the rice, bring to a boil. Turn off and let the rice steep, covered, for about 15 minutes.
Add the vinegar with sugar, tofu and red cabbage to the still hot rice, mix, spread out on a baking sheet and let cool.
Remove rice in about 8 equal portions, form each into balls and shape best with an onigiri mold.
Place a nori rectangle around the bottom of each onigiri, arrange on a plate and serve onigiri with red cabbage and smoked tofu with soy sauce to taste.