Marc wanted to create a car that was simple, likeable, and fun. Built at the historic Carrozzeria Ghia in Turin, Italy, Marc developed the car via drawings, followed by computer models, and finally created a clay model to perfect complex surfaces.

Every component of the car was designed and fabricated from scratch from workshops all over the world; the tyres were custom-made by Pirelli in Italy, for example. The composite exterior featured seamless shapes and deceptively simple surfaces, including a wraparound, retractable trunk that opens like a drawer, and door handles that are simple aluminium buttons surrounded by translucent plastic rings, which illuminate when remote locking is activated. The doors themselves open to expose a completely open 'pillarless' interior. The windows were designed to allow as much light as possible to enter. The single horizontal headlight and rear light are powered with LEDs which, at the time of making, was a state-of-the-art technology never seen in automotive design. The entire interior ceiling is illuminated with optical fibres. Other innovations include a hovering instrument panel that adjusts up and down in its entirety.

The car interior is a primary focus, relating strongly to Marc's signature furniture designs. It is predominantly silver and white and features a variety of textures and materials, including aluminium and rubber. The floor, which remains completely flat due to the front-wheel-drive technology, curves smoothly up into all vertical surfaces. The instrument panel and seats appear to float in the interior, designed to accentuate the feeling of spaciousness in a car that is in fact smaller than any other Ford production vehicle.  Further merging design with functionality, the front seats swivel 90 degrees to facilitate entering and exiting the vehicle. Marc's stamp is on every element of the design, from the strikingly reduced and intuitively simple instrumentation to Ikepod dials, switches, wheels and even the tread on the tyres.

The O21C was first unveiled at the 1999 Tokyo Motor Show where it was awarded Best Concept Car.