2ozblood orange soda, such as San Pellegrino Aranciata Rosa
1dried blood orange slice,for garnish (optional)
Add rum, grapefruit juice, lime juice, and passionfruit syrup to an ice-filled cocktail shaker. Shake vigorously for 30 seconds. Strain into an ice-filled cocktail glass. Top with blood orange soda. Garnish with dried blood orange slice.