According to an article on Gamasutra.com, Dead or Alive: Dimensions was the second best selling game for the past week in Japan. It was able to sell an estimated 23,078 units in the week. The #1 game sold for the week was for the PSP, titled "Akiba Trip" at 58,150 units. Since Akiba Trip is a PSP exclusive title, it can be said that Dead or Alive: Dimensions was the top selling Nintendo 3DS title for the week.
Congratulations goes out to Koei-Tecmo of Japan and Team NINJA. Hopefully the game has a good trend of sales as the Nintendo 3DS install base increases.
Link: http://www.gamasutra.com/view/news/34851/Akibas_Trip_Dominates_Japanese_Software_Charts.php