Arrange the watermelon cubes in a single layer on a serving platter.
Place one cube of feta on top of each piece of watermelon.
Fold a fresh mint leaf and carefully thread it onto a toothpick.
Push the toothpick through the feta and then into the watermelon. Repeat until all 24 skewers are assembled.
To prepare the balsamic glaze, combine the balsamic vinegar and sugar in a small saucepan.
Heat over medium-high heat until the mixture begins to simmer.
Reduce the heat as necessary to maintain a steady simmer and cook for approximately 5 minutes, stirring continuously, until the mixture has reduced by nearly half.
Remove the glaze from the heat and allow it to cool for 1–2 minutes. Do not leave it too long before using, as it will continue thickening as it cools.
Spoon or lightly drizzle a small amount of balsamic glaze over each of the Watermelon Feta Mint Skewers.
Serve immediately while the watermelon is fresh and juicy.