The Blue Seven is an unlockable Kart body in Mario Kart 7. It's frame is very aerodynamic, resembling a very high-speed race car. As a matter of fact, Speed is the Blue Seven's main advantage, with poor Acceleration leveling its capabilities.
The basic color of the Blue Seven is a shade of blue, which suits the name fairly well. The front section of the car has white stripe running down the center, with the Character's logo in the center of it. A thin gray strip of metal rests right underneath the cart's two yellow headlights, which slant accordingly with the hood. Also, a small windshield is provided in front of the black steering wheel and seat. The Blue Seven's frame slopes nicely around the wheels, both front and back. In between, another decal of the player's icon can be seen, along with an underlying metal strip. The rear of the Kart boasts an aerodynamic yellow fin fastened with a gray metal structure. It's about two feet long, with a black stripe in the center. A white circle with a black 7 on the right side of the fin gives the Blue Seven the second part of its name. Flanking the fin are two yellow exhaust pipes, cut to curve slightly towards each other. Finally, two red taillights and multiple light blue lights are on the rear bumper, lined my more metal at the edge.
Collect a certain amount of Coins. Unlocked at random...
The "Seven" in the Blue Seven's name is very likely linked to the title of the game its in (Mario Kart 7); the 7 design on the fin is exactly alike to the Mario Kart 7 logo seven.
The Streamliner from Mario Kart DS is thought to be the basis of the Blue Seven, as they bear a striking resemblance to each other. Both have almost the same exact shape, painted blue, and have a white stripe in the center. People believed that it was a remake of the Streamliner before Mario Kart 7 was released.