Shinkansenspotter

Chill a cocktail coupe in advance.

Add the rye, elderflower liqueur, umeshu, and Fernet Branca to a mixing glass.

Introduce a splash of rice vinegar and 2 dashes of grapefruit bitters.

Fill the mixing glass with ice and stir until well-chilled.

Strain the mixture into the prepared coupe.

Garnish with a twist of grapefruit peel, expressing its oils over the drink before placing it in the glass.