DS and "Kanji Brain"
From an article comparing top sales:
Software Sales - This Week | Total Sales
1.) Common Knowledge Training (NDS, Nintendo) - 102,240 | 451,106
2.) Pokémon Diamond (NDS, The Pokémon Company) - 78,744 | 1,682,896
3.) Kirby: Squeak Squad (NDS, Nintendo) - 77,949 | 244,081
4.) Pokémon Pearl (NDS, The Pokémon Company) - 65,574 | 1,423,990
5.) Kanji Brain (NDS, IE Institute) - 33,932 | NEW
6.) New Super Mario Bros. (NDS, Nintendo) - 27,361 | 3,393,921
7.) More Brain Age (NDS, Nintendo) - 24,166 | 3,412,008
8.) Winning Eleven DS (NDS, Konami) - 23,653 | 112,928
9.) Ridge Racer 7 (PS3, Bandai Namco) - 21,655 | NEW
10.) Gundam: Target Sight (PS3, Bandai Namco) - 21,310 | NEW
And... DS is region free! I know what I want to Christmas now.
There's just one small problem: there is a bunch of kanji games for DS, so identifying the one may prove difficult. Known before are Rakubiki Jiten (aka: "DS Rakuhiki Jiten: Kanji Sono Mama") and KanKen DS (aka "Zaidan Houjin Nippon Kanji Nouryoku Kentei Kyoukai Kounin: KanKen DS"). After a short googling it appears that what they really mean is "Zaidan Houjin Nippon Kanji Nouryoku Kentei Kyoukai Koushiki Soft: 200 Mannin no KanKen: Tokoton Kanji Nou". I do not know how it is customarily shortened. The jacket says "tokoton kanji nou", so perhaps it's Tokoton. The game is available at Play-Asia.
BTW, I suspect that the game got into the best-selling list because of Japanese parents who buy it for their kids. Kids can't be crazy enough to buy them on their own. On the other hand, I'm sure we can find 30,000 Americans with midlife crisis and Japanese fetish at any given week. Maybe they are who buys all those games.