For the blueberry syrup:

1. Place the blueberries in a large jar, and cover with the sugar and the water.
2. Place the jar in the fridge and let it rest for 4-6 hours or overnight to let the sugar draw the juices out of the blueberries.
3. When done resting, give it a good stir and add a bit more water if you want it less sweet.
4. For a faster option, you can muddle the blueberries after they thaw to speed up this process, or microwave them briefly and use the purple blueberry juices that run off.

For the matcha:

1. Heat the water in a small jar with a lid. Add the matcha powder, cover, and shake until smooth.
2. Fill a large glass with ice. Pour the matcha over the ice, and then add the oat milk.
3. If you want distinct color layers, pour the oat milk over the back of a spoon.
4. Finally, pour 1-2 tablespoons of the blueberry syrup into the glass and watch it sink to the bottom.
5. Stir just before serving to distribute the blueberry flavor throughout!