How about this one?
A Chevrolet Corvette 1971:
http://trackmania-carpark.com/car.php?id=2157 And Nue Houjuu;
Imagine the car, the rims, the windshield, is black. But leave the chrome parts as they are, chrome.
Have Nue on both sides of the car, pointing her trident towards the front, like she is ready to attack.
On the hood, have her lie on her belly, and have her look forward and up, or something like that.
Some other suggestions:
(the car is colored scarlet = Flandre) (sky blue = Cirno) (Green = Meiling) just to name a few : P
But how does it work; do you post your finished "Itasha" as a skin, and everyone can download the skin, and put it on the car? Or?
(Because if that is the case, I would look forward to try trackmania, with one of these "Itashas")