Whisk together all the mochi dough ingredients in a heat resistant bowl. It should be thinner than the typical consistency of pancake batter. Let the batter rest for 10 minutes. Run through a fine mash strainer to remove any clumps if necessary.
Fill a steamer pot with 2 cups of water and place the bowl of mochi batter into the steamer. Cover the steamer and place the steamer on a stove. Bring the water to a boil and then turn down to medium heat or to a gentle boil. Steam for 12 minutes. When the mochi dough is cooked, the center of the dough should be set without any runny liquid.
Remove the bowl from the steamer and transfer the cooked mochi dough into another clean glass or ceramic bowl with a spatula. Cover the bowl with a lid or plastic wrap and cool completely in refrigerator. Approximately 2 hours.
Meanwhile, add coconut shreds and agave nectar (if any is used) into a food processor. Pulse to chop the shreds into smaller pieces but not powder. Transfer the prepared coconut shreds into a bowl and set aside.
Wearing disposable kitchen gloves, evenly divide the mochi dough into 8 pieces. Approximately 35 grams for each piece. Use your fingers to shape each piece into a smooth ball and then flatten it between palms to form smooth disk. Place one piece of mango cube in the center and then wrap the edge of the dough around the mango. Gently pinch the opening of the dough together to close and form a smooth ball again.
Place and roll the mochi ball in prepared coconut shreds. Coat evenly. Transfer the prepared mochi in cupcake liners. Set aside.
Repeat step 5 and 6 to finish all mochi dough. Refrigerate at least 30 minutes before serving. These mocha balls can be stored in the refrigerator up to 3 days. Longer time storage will make the mochi balls stiff.