KASHIWA, Japan—In a shopping mall outside Tokyo, people kick the tires of showroom models lined up under glossy posters. A Hummer SUV is shown in an alpine setting, a Cadillac stands out against a satiny black background. A Chevrolet Suburban is crossing a river bed.

Chevys are parked between olive-green or bright-yellow Hummers and wine-red Caddies with gold rims. Salesmen talk up the leather seats and offer test rides. The franchise is buzzing on this, the last day of a "Chevrolet Fair" campaign. Buyers get a free halogen...