In a small saucepan, combine 15g of rice vinegar, 8g of sugar, 8g of soy sauce, and 8g of water. On a separate burner, bring the mixture to a gentle simmer while stirring to dissolve the sugar, then turn off the heat. Finely chop 15g of onion, soak it in water for 5 minutes, and drain thoroughly. In a clean small bowl, mix 25g of mayonnaise, 20g of yogurt, and the onion, then place it in the refrigerator.