Traditionally the big two car brands in Japan are Toyota and Nissan. In 1975 for example, their combined sales accounted for nearly 70% of the Japanese market! (See chart below). Understandably, that hasn't been maintained. In fact, Nissan has slipped to third occasionally of late; the italicised figures below show when on this chart that occurred. The 2011 sales figure is for the first six months of the year. All sales figures are in thousands, so please add three zeros:
The 2011 figure is ugly for Toyota, although in any other context over a quarter of the market for a brand would be considered good. Nissan on the other hand is making a bit of a comeback with more interesting cars than many of its rivals.
When you add all the other Japanese brands to these two, you realise how insignificant import brands are in the country. With a mixture of crafty measures and strong loyalty, foreign makes remain on the periphery.