Nana is based on the manga series of the same name by Yazawa Ai. Okay, loosely based. Pretty much, you're playing an animated board game with refences to the manga in the cut-scenes and stages. You play as Nana or Hachi or create your own character. Other characters are unlockable to play. You also get to buy accessories and decorate your room with your winnings.
Despite being in Japanese, it's pretty easy to figure out the controls. O is what X normally is and X takes over for O. You get three stages to play and it's game over if you come in last place. Avoid this by playing against three other characters and making sure to come in first or second place in the first two stages and first place in the third stage. The game just accumaltes your winnings so if you do lose, just keeping playing instead of starting over.
This game is a brain vacation. That means that you can play this game and not get your heart pumping at marathon levels. Just press O and watch the pretty pinkness commence. Yes, pinkness. If you don't like pink, stay away. ^^ :p
PS: The full title of the game is Nana: Subete wa daimaou no omichikibi!?, which translates to Nana: Everything is the Demon's Plan. O.O :3