Woah, second gen are all leaving the hive.
It really shows the impact of Tokyo Dome. Dreams have been fulfilled and it's time for a new challenge, either in or outside AKB48.
Sato Natsuki's been overlooked ever since 0ji59fun turned into AKBingo. Everybody recognizes her vocal talent (once again confirmed during the karaoke concerts), yet she never managed to really step in the spotlight, like she mentions in her entry. With that in mind I can totally understand her decision. On the other hand, I'd be a loss if she leaves the entertainment industry forever, but I guess she doesn't have the back-up/following to pursue a solo singing career.
So yeah, best of luck to Natsuki in her future career.
edit: With Yuka and Nacchi gone, and Sae to China, the number of 2nd gen members is down to six...