Cut a grapefruit into quarters and add one of the quarters to cocktail shaker. Add in the pomegranate seeds then use muddler to press grapefruit and pomegranate in order to release their juices and oils.
Add ice and gin to cocktail shaker and securely place the top on it. Shake vigorously for about 10 seconds to fully chill and combine the liquid.
Strain liquid into a coupe glass and top up with chilled tonic water. Garnish with a wedge of grapefruit and pomegranate sides, if desired. Enjoy responsibly!