Order sushi-quality tuna in advance from your fishmonger. Freezing the tuna for three hours before preparing will help you cut thinner slices.
In a small bowl, combine the vinegar, sugar, lemon juice, soy sauce, and black pepper to make a ponzu sauce. In a separate bowl, combine 1 tablespoon soy-sauce mixture with mayonnaise; set aside.
Remove tuna from freezer; slice into thirty-six 1/8-by-1 1/2-by-2 1/4-inch rectangles. Arrange slice of tuna on top of an orange slice. Drizzle with 1/4 teaspoon of mayonnaise mixture; garnish with several capers and cilantro. Repeat with remaining ingredients. Serve immediately.