In a heatproof bowl, whisk together 1 cup of glutinous rice flour, 1/4 cup of granulated sugar, and 2 tablespoons of watermelon powder. Gradually pour in 3/4 cup of room temperature water, mixing until smooth.

Place the batter in a steamer basket, cover with a lid, and steam over boiling water for 15 minutes until the mixture is glossy and sticky.

Remove the bowl after steaming and cool for 5 minutes. Dust hands and surfaces with cornstarch and knead the warm dough until smooth.

Flatten the dough to 1/2-inch thickness and cut into triangle shapes resembling watermelon wedges. Press chocolate chips or sesame seeds into each piece for decoration.

Transfer the shaped mochi onto a cornstarch-dusted plate and cool completely for about 10-15 minutes.