Gather the ingredients.
Soak the azuki beans in water overnight to soften. (While the beans won't have completely softened, they will have expanded considerably). Drain.
About 2 hours before making the soup, place the dried lotus seeds in a bowl with enough water to cover.
In a medium saucepan, bring the 6 cups of water with the tangerine peel to a boil. (The soup can be thicker or thinner as desired. We usually start with 6 cups of water, and then add more boiling water at the end with the brown sugar if we want to thin it a bit.)
Turn the heat down, add the adzuki beans and lotus seeds and simmer, partially covered, for 1 to 1 1/2 hours, until the beans are softened to the point where they are just beginning to break apart.
Add the brown sugar and stir until dissolved. Taste and add more sugar if desired. (We usually start with 1/3 cup and then add more, 1 tablespoon at a time, as needed). Thin the soup by adding boiling water if desired.
Remove the dried tangerine peel before serving.
Serve the red bean soup hot or cold.