Cut the grass jelly into bite-sized pieces and refrigerate. Bring water to a boil and add the sweet potato balls. Cook until they float and are done, then remove and set aside. (Only cook as much as you will eat, as they harden if stored.) Cook the red beans in a rice cooker until tender, then set aside.

In a pot, bring 1 2/3 cups (400 ml) water to a boil, then reduce to low heat. Add the dark brown sugar and light brown sugar, stirring until dissolved. Let cool, then refrigerate. Adjust sweetness to taste.