Some of us are old-fashioned to 2005-era tactics of downloading Bittorrents of game music - "game mp3s" if you will.
Of course, you should only do this if you own the soundtrack legitimately and merely are too lazy to rip it.
Or at least own the game itself.
Or can't purchase the CD legitimately without import - which doesn't apply to you, you're in Japan! Go buy some! ...although I was just looking myself and yeesh, some soundtracks really do have it out for your wallet, especially the ones that come on multiple CDs. Ar nosurge follows the tradition of the other Ar tonelico games of having the soundtrack & vocal CDs separate so you can pay twice or thrice, I see. I did pick up ~100 USD worth of random music legally though, so hey, doing my part.