Combine mochi rice flour and unsweetened cocoa powder in a bowl and mix.
Add protein powder, sweetener, and salt, then mix well.
Gradually pour in the milk to form a dough.
Divide the dough into 4 portions and shape into balls.
Place parchment paper in a steamer and put the dough balls on top.
Steam on high heat for 15 minutes.
Let it cool, and if desired, sprinkle cocoa powder on top to finish.