Step 1.
- In a blender, puree the watermelon until smooth.
Step 2.
- Strain the watermelon puree through a fine mesh sieve into a bowl, discarding the pulp.
Step 3.
- In a highball glass, muddle the mint leaves with the lime juice and simple syrup.
Step 4.
- Add the fresh watermelon juice and sake, and stir gently to combine.
Step 5.
- Fill the glass with ice and top with club soda. Stir lightly to mix.
Step 6.
- Garnish with a mint sprig and a wedge of watermelon.