The most recent figures from Japanese sales tracking authority Media Create show that the 3DS has sold 12,752,731 units in the island nation. By contrast, the Wii has sold 12,698,878 units. As GamesIndustry points out, with the 3DS enjoying its golden years and the Wii slowly fading from memory, it seems likely that the handheld will maintain its lead.
There are many reasons for the success of the 3DS, but most notable is the sales juggernaut known as Monster Hunter 4. Japan apparently loves murdering giant beasts, as the game has remained in Media Create's top sales spot since its debut. Buoyed by this hyper-popular game, the 3DS managed to sell 159,388 units in Japan during the week of September 16 alone - an impressive feat, given that total hardware sales for the period were only 187,773.