In a bowl, mix rice with vinegar. Set aside. Place a sheet of nori shiny side down and spread a heaping tablespoon of rice over nori. Mix tuna, cucumber, carrot, and daikon together. Place on a plate and divide into 12 sections. Then place one section on top of rice along edge. Fold edge of nori sheet over filling, pressing firmly to start a tight compact roll. Roll to close. Slice roll into 6 pieces. Arrange on plate and garnish with wasabi mayonnaise and sushi ginger. Repeat with 2nd sheet. Divide among 2 plates.