The following chart will be pretty boring if we look at the recurring names which make at least an appearance, but it won’t if we take in account that positions changed a lot in the last years, in particular at the top of the chart.
Here the Top 10 (Famitsu data):

1. Pokemon Black / White: 2.637.285 (2 days) | 2010
2. Final Fantasy VIII: 2.504.044 (4 days) | 1999
3. Dragon Quest IX: 2.343.440 (2 days) | 2009
4. Dragon Quest VIII: 2.236.881 (2 days) | 2004
5. Monster Hunter Portable 3rd: 2.146.467 (5 days) | 2010
6. Final Fantasy VII: 2.034.879 (4 days) | 1997
7. Final Fantasy IX: 1.954.421 (3 days) | 2000
8. Dragon Warrior VII: 1.862.065 (2 days) | 2000
9. Final Fantasy XII: 1.840.397 (4 days) | 2006
10. Final Fantasy X: 1.749.737 (2 days) | 2001

I specified the days counted for the sales, because even though it’s a convention that these data pertain the first week of sales, the release day (usually thursday) can often vary, from the wednesday of Monster Hunter Portable 3rd to the Saturday of many other games (usually to prevent absenteeism in schoold and workplaces in case of really popular titles); this factor must be considered when the chart is read in order to weigh differently the openings.

Anyway, Pokemon, Final Fantasy and Dragon Quest took the 90% of the positions; the Capcom hunting game is a newcomer in the best-seller club reaching very high levels with the latest entry and becoming a phenomenon in its homeland; Monster Hunter Portable 3rd has indeed gained the 5th position on the list by selling over 2 millions of copies within the first 5 days after the launch (a huge increase compared to the 2nd G which opened with “only” 823.265 copies sold and the previous chapter with 746.313 copies), with huge lines outside shops and a big press coverage by Famitsu and other important Japanese magazines. However 5 days weren’t enough to reach Pokemon Black / White levels, which stabilized the record of all time in just 2 days, with a constant flow of people buying the game throughout the weekend. So, 2010 has been very fruitful for gaming industry in Japan, at least considering million-seller games. Mainline Pokemon games have always shown very big debuts after the mania was born in mid-90s, but such numbers were totally crazy for an entertainment product, at par with Halo series openings in North America; Pokemon Diamon / Pearl stands just outside the chart with 1.586.360 copies at launch (11th position), while Pokémon Gold / Silver and their 2009 remakes (HeartGold / SoulSilver) follow slightly lower with 1.425.768 and 1.408.980 copies sold respectively.

Along these two series, also Dragon Quest had its best debut in this generation, with Sentinels of the Starry Skies, the 9th chapter, appeared on DS; the game was able to sell more the 2.3 million units within the first 48 hours, a mark which allowed it to become the best selling entry in the famous jRPG saga (its LTD is 4.152.985 copies sold, with additional 141.671 copies sold by the Ultimate Hits version).
As a matter of fact, Dragon Quest has had a constant presence in this chart and has grown over time until the peak one year and a half ago; other chapters make their appearance in lower positions: the VI for SNES and for DS (16th and 25th, with 1.274.857 and 909.981 units sold respectively); the V with its remake for PS2 (19th, 1.048.925 copies) and a lot of other remakes, spin-off and mainline entries.

On the other hand, Final Fantasy is decreasing quite dramatically episode after episode; Final Fantasy VIII set a milestone in the chart being undefeated for 11 years with over than 2.5 millions the first 4 days on the market while VII and IX started with nice numbers. But since Final Fantasy X, debuts have always been lower than the PS1-era, with a new minimum level reached by the XIII episode on PS3, which started with 1.516.532 copies during 2009 Christmas holidays and ended below the 2 millions mark.

In conclusion, Pokemon and Dragon Quest have  grown in this generation thanks of the releases on a very successful platform, the DS, starting from a solid base; instead, Monster Hunter has recently seen an explosion coming from modest outcomes  on PS2 and during the first period on PSP while Final Fantasy is slowly laying down the crown.

By the way, other important brands have one or more title in the chart scrolling down the positions: Resident Evil with the second and the third chapter on PS1; Yu-Gi-Oh in the good old days on Game Boy; Super Mario Brothers on DS and Wii and so on. The rest of the chart can be seen by clicking here.