In a cocktail shaker or an old jam jar with a lid, combine the Yakult, soju, salt and a handful of ice. Shake until the outside of the container is cold.
Taste the yogurt soju and add more Yakult or soju as needed.
Place a handful of fresh ice in your serving glass, then strain the yogurt soju into the cup. Top off with sparkling water, give it a stir, and serve.
Recipe Notes
I like to use plain soju and sparkling water, but feel free to use flavored soju and/or ginger ale or lemon lime soda instead.