Finished this game today so thought I'd share a few thoughts about the story mode here. I've got a bunch of pics of the game as well and may place them on my site at a later date.
The story mode is about 3 girls who go around playing mahjong matches against a variety of villains. Of course much fan service and nudity is the result of these matches though the nudity is comedic and mainly of the "barbie doll" variety.
There are 4 main stages in the game. The first stage starts you off in a school where you can wander the hallways and into different rooms where you may find some dude and his porno collection or even into the girls locker room. :-" A couple of your mahjong opponents in this area are the captain of the girls volleyball team (complete with volleyball mini game) and a teacher who suddenly grows 100 feet tall. On to stage two.
In stage 2 you end up inside a wrestling arena run by a dominatrix and some dude in a yellow banana hammock. There is a wrestling mini game here complete with some very interesting grappling moves.
Stage 3 takes place inside a magic castle of some sort. Here you'll meet Alice in wonderland who you will have to play a card battle game against before your mahjong match. Another interesting character in this stage is a knight in golden armor who one of the girls falls in love with. He gets her back to his place naked and into bed when she sees by the reflection in the mirror that his armor has no back on it and he's naked underneath. Nothing a game of mahjong won't fix though. Um....yeah.
Stage 4 takes place against a bunch of half beast/half girl opponents. You'll get a bit of help toward the end.
Overall, I found the game to be a lot of fun and the story kept me interested all the way through. I think just about anyone can follow what's going on without knowing Japanese. The mahjong rounds in the game are fairly easy and the only real difference in the opponents is the amount of points they start out with. Hope this was just enough info for you to want to give it a try.