In a mixing bowl, combine cream cheese, heavy cream, and sugar. Whip on medium speed until smooth and creamy, about 2–3 minutes. Fold in fresh blueberries and set aside.

In a microwave-safe bowl, mix mochiko flour and water until no lumps remain. Microwave on high for about 2 minutes. Stir, then microwave for another minute until slightly translucent and sticky.

Dust hands and work surface with cornstarch. Divide dough into portions, flatten each into a 3-inch disk, fill with blueberry cream filling, and pinch edges to seal.

Place shaped buns on a lightly dusted plate and chill in the refrigerator for about 15 minutes. Serve cold or at room temperature.