Combine all ingredients in a mixing glass over ice and stir until chilled. In a rocks glass, lightly muddle shiso leaf to release aromatics, then add a large ice cube. Strain cocktail into the rocks glass. Express grapefruit peel over cocktail, and discard.
*White Sesame Cane Syrup
Toast 80 grams white sesame seeds until golden, stirring constantly so as not to burn. Combine with 1,100 grams cane syrup in a sous-vide silicone bag. Preheat water bath to 155 degrees Fahrenheit, place bag in heated water, and let cook for 1½ hours. Remove and place in ice bath until syrup cools down. Pass through cheesecloth to strain, then vacuum-seal and store in refrigerator.