I know this response is kind of late, but the reason you didn't know it was probably because it was a Xbox 360 exclusive for many years. They did make a PS3 version not that long ago but I doubt they marketed that much over there, it must have been easier and cheaper to market it to PS3 owners in the west, who already knew about the game but couldn't buy it because it wasn't on their system, then to start from scratch on the japanese market where no one knew the game.
Which would be rather odd, unless they thought the game wasn't very good. Pretty much all the other Xbox 360 exclusives were marketed heavily when they put out their PS3 versions. The publishers of those games wanted to make some profit from their work I guess!
Actually, I was wrong. Looking up details of the release online, apparently it was out for both Xbox 360 and PS3 in Japan but internationally it was a Xbox 360 exclusive for some reason.
The west only saw it on PS3 April of this year, with the advent of the Director's Cut, which was never released in Japan. Peculiar at first glance, until you see how it truly did not sell over there: exhibits one
Not every game is a bestseller, but as for why this one in particular did not sell at all over there, I cannot fathom. Maybe it was a foregone conclusion. You say you never heard of it, so maybe the publisher never advertised it because it didn't think it would sell, then when it did not sell due to the lack of advertisements, they gave themselves a pat on the back for being right.
Speaking of publishers, the original release was published in Japan by Marvelous Interactive, but since the Director's Cut never came out over there, there seems to be no ties between Marvelous and the Director's Cut, and that's the one coming to PC, maybe Rising Star might retain the rights over there as well?