After cooking the Japanese rice, bring the rice to room temperature in a large bowl.
Mix together the sugar, salt, shredded par-boiled carrot and vinegar until the salt and sugar are completely dissolved. Pour the mix slowly over the rice.
With a rice paddle, fold the vinegar mixture into the rice carefully. Do no overmix, and do not let the rice become soggy. Do not refrigerate.
Heat katsuobushi broth to boil in a generously sized pot. Remove from heat. Place deep-fried tofu pouches in pot for 5-6 minutes then drain. Allow to cool. Squeeze the tofu pouches and gourd strips dry. Set aside.
Carefully open the deep-fried tofu pouch, then pick up enough rice to make a small, oval-shaped ball; gently slide the rice ball into the pouch.
Fold the sides in and top flap over the rice to close pouch. Repeat with remaining rice and tofu pouches. If you like, serve them with amazu shoga.