Prepare the kashiwa leaves. If using dried leaves, rehydrate them in water. If using vacuum packed leaves, rinse them with water and pat dry with a paper towel. Set it aside to use later.
In a bowl, mix the joshinko rice flour, mochi flour, and sugar. Slowly pour the water and stir until it forms a paste.
Line a steamer with parchment paper or cheesecloth, and put the paste inside. Steam for 20 minutes.
While waiting for the mochi, divide and roll the red bean paste into 8 equal balls.
Take the mochi out of the steamer and knead until it forms a ball. Divide into 8 equal pieces.
Take one piece of mochi and flatten it out into an oval. Place a red bean paste ball in the center and wrap it with the mochi. Make sure the sides are completely sealed.
Place each mochi on the shiny side of the kashiwa leaf and fold the leaf over the mochi. Put them back in the steamer for an additional 5 minutes. Let them cool completely before eating.