I have seen AKB0048 S2 ep13 at the end 14th Atsuko Maeda is Motomiya Nagisa and Sono Chieri become center nova. Maybe the best episode of AKB0048 Next Stage is episode 13.

And the romantic moment when mamoru catch Yuka when she fall. 

And you can watch the video at

http://www.youtube.com/watch?v=NJU-bMxvXrQ

And some photos