How to Make It
In a small saucepan, bring the sugar and water to a boil. Simmer over moderate heat, stirring, until the sugar dissolves, 2 to 3 minutes. Let cool, then transfer to a jar, add the grapefruit zest and refrigerate overnight. Transfer the syrup to a blender, add the shiso and puree until smooth, 1 minute. Strain the syrup through cheesecloth into a jar; refrigerate until ready to use, up to 2 weeks.
In a large pitcher, combine 4 ounces of the grapefruit syrup with the sake, green tea, elderflower liqueur, whisky, lemon juice, yuzu juice and bitters. Refrigerate until chilled, about 2 hours. Fill the pitcher with ice and stir well. Pour the punch into 8 chilled rocks glasses or stemless wineglasses and garnish with the apricot, plum and ginger slices and smacked shiso leaves.