For an extra layer of flavor, try adding a teaspoon of Dijon mustard to the mayonnaise before mixing. If you don't have Japanese mayonnaise, regular mayonnaise works well, but consider adding a touch of sugar for sweetness. Feel free to adjust the amount of mayonnaise and rice vinegar to suit your taste. Some people prefer a tangier salad, while others like it creamier. This potato salad can be made ahead of time and stored in the refrigerator for up to 2 days. The flavors will meld together beautifully over time.