I agree Laoldar, this game should be priced at 4 million copies sold over lifetime. First, there is the fact how big a series Dragon Quest is in Japan. Consider that Dragon Quest VIII was the best selling PS2 game over in Japan with 3.6 million copies sold.
Add in phenomenon that the DS is in Japan, the DS holds spots 4-7 on the top 10 best selling games of all time in Japan (the top 3 being the GB and GBA pokemon games) and this game will probably sell 4 million copies over its lifetime, if not more. Also, consider that this game will also be released outside of Japan, possible bumping the total sales up to 5 million if the conditions are right.
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Add in phenomenon that the DS is in Japan, the DS holds spots 4-7 on the top 10 best selling games of all time in Japan (the top 3 being the GB and GBA pokemon games) and this game will probably sell 4 million copies over its lifetime, if not more. Also, consider that this game will also be released outside of Japan, possible bumping the total sales up to 5 million if the conditions are right.
Sources:
http://vgchartz.com/japtotals.php