About the Black Stones...

(some spoilers ahead)
The manga Nana's primary focus is centered on the relationship between the two girls named Nana, and their own relationships, however another primary focus within the story's plot is the development of Oosaki Nana's band -- Black Stones (BLAST).

The members of BLAST include: (from left to right)

Oosaki Nana, vocals

Terashima Nobuo (Nobu), guitar

Okazaki Shin'ichi (Shin), bass

Takagi Yasushi (Yasu), drums

The band was formed while Nana, Yasu and Nobu were in high school, and back at that time Honjo Ren (currently of rival band Trapnest) was the bass guitarist for BLAST. Ren and Nana were dating back at the time that the band was formed, and when Ren left for Tokyo and Trapnest, the band split up. Nana swore she would not simply follow Ren to Tokyo so when he left, they broke up as well.

Now in Tokyo, Nana wishes to make a name for herself and to surpass Trapnest and their fame. Nobu joins her in Tokyo and Yasu (who had become an attorney after high school) decided to get back with BLAST. Now short a bassist player, the group set out to find a replacement for Ren....here is where Shin fits into the picture. A brilliant and talented musician, Shin truly impressed the Black Stones. The first thing that Nana noticed about Shin was that he played the bass very similar to the way Ren did. When questioned about this he stated that he looked up to Ren's musical ability. Nana asked Shin to 'surpass Ren' and he was then tapped as the next member of the Black Stones.

Currently the band has signed a record deal with GAIA Records and they are living the life of celebrities under the magnifying glass. Nana and Ren (who are now back together) are having to learn how to deal with having a real relationship when the details of it is plastered throughout the media. Nobu is having his own problems with women as well as the weight of knowing his family is counting on him to one day run the family business. Yasu is simply trying to hold everyone (including himself) together, especially as he contends with his own romantic feelings for Nana, and his brotherly relationship with Ren. Finally Shin has a secret past regarding his parentage that no one really knows all the details of, and he is currently in the middle of a secret affair with the lead vocalist of Trapnest - Serizawa Reira.