Select Attack mode and a driver of your choice, then select Tsumuji as your opponent. All you've got to do now is finish in first place and his car will become available.
Race the Vestal
Beat the game with every car. You can save after you beat the game with a car, but you cannot use any continues. Now you can race as Maki's six-wheeled vehicle from the end of the game.
Race the B-Vestal
Beat the game using Maki's Vestal and the B-Vestal will be revealed.