Like most Final Fantasy games in Japan, Final Fantasy XIII is subject to a huge sales drop off for it's second week sales. According to Media Create, Final Fantasy XIII has sold 189,000 in it's second week, which is only 12.6% compared to it's previous week sales of over 1.5 million.
For comparison, both FFX and FFXII had second week sales of about 13.3%. That difference may not sound very significant, but considering that both FFX and FFXII had larger first week sales than FFXIII, combine that with FFXIII's second week sales being lower than both of those games, the chance of it selling 3 million copies in Japan is looking slim, unless it continues to sell in excess of 100,000 copies for the next few weeks then it might be possible. But alas, if history repeats it's self, then the third week sales will be roughly 1 third of the game's second week sales.
Final Fantasy XIII currently sits at 1,690,000 copies sold in Japan.
Source: FF-XIII
For comparison, both FFX and FFXII had second week sales of about 13.3%. That difference may not sound very significant, but considering that both FFX and FFXII had larger first week sales than FFXIII, combine that with FFXIII's second week sales being lower than both of those games, the chance of it selling 3 million copies in Japan is looking slim, unless it continues to sell in excess of 100,000 copies for the next few weeks then it might be possible. But alas, if history repeats it's self, then the third week sales will be roughly 1 third of the game's second week sales.
Final Fantasy XIII currently sits at 1,690,000 copies sold in Japan.
Source: FF-XIII