Clean 300 g strawberries and cut into pieces. Cut 300 g melon meat into pieces and core. Finely mix watermelon and strawberry pieces, sugar and grenadine syrup in a blender. Add lemon juice and yogurt and mix briefly once. Chill the soup.
Halve 100 g strawberries and cut 300 g watermelon pulp into cubes.
Pour the cold soup into cups. Top with strawberries, melons and blueberries. A nice serving option: place the cups on deep plates with crushed ice and serve.