Because you don't use water, it's so soft and chewy even after some time.
My mother used to make this for me. I've always wanted to post this recipe here. Today, this recipe has become a "mother's recipe" for me to teach my daughters.
You could also make this with "Dango Flour." In that case, because it's not 100% glutinous rice, reduce the amount of tofu to 200 to 220 g. It's tasty either way.
Enjoy Japanese food around the world.