Rinse the strawberries and remove their stems. Each berry should remain whole beneath its trimmed top.
Portion the white bean paste into 30 g pieces and form each into a ball. Even portions create a consistent layer around the berries.
Press a paste ball into a flat round and position a strawberry in its middle with the pointed end downward. The paste should extend around the berry so it can cover the sides.
Bring the paste around the fruit, round the covered berry, and set it aside. The strawberry should sit inside a continuous bean-paste shell.
Combine the shiratamako, sugar, and water in a large heatproof bowl, stirring thoroughly. The mixture should look evenly blended rather than separated into dry flour and liquid.
Cover the bowl with cling wrap and microwave for 1 minute and 30 seconds to 2 minutes, depending on your microwave. Expect a mixture of floury-looking areas and portions beginning to turn sticky and doughlike.
Remove the bowl, work the mixture thoroughly with a wooden spatula, and microwave for another 1 minute. The dough should now look translucent rather than chalky and opaque.
Spread potato starch generously over the rolling mat and transfer the cooked mochi onto it. The starch should separate the sticky dough from the mat.
Separate the mochi into 6 portions and roll each into a circle approximately 10 cm across. Each round should provide enough dough to reach around a filled berry.
Set a bean-paste-covered strawberry in the center of a mochi circle with its tip pointing down. The broad stem end should face upward toward the edges you will gather.
Coat your hands well with potato starch and bring the wrapper edges up around the filling. The mochi should surround the paste without leaving an exposed gap at the sides.
Pinch the gathered edges together with starch-dusted fingers and gently round the daifuku. The meeting point should form a closed seam with no visible filling.
Finish wrapping the remaining covered berries in the same way. Each finished piece should have a rounded exterior and a sealed opening.