Arise!
I've been hunting for this story I remember reading.
Main character is Rukia, and its about the time inbetween Ichigo losing his powers and regaining them. It focuses on Rukia in the Gotei 13, the return of Shinji to the 5th Division(one scene I remember is Shinji abruptly showing Rukia his mask, and Rukia's reaction is to say that Ichigo's reiatsu is higher), and Rukia becoming Vice-Captain.
EDIT: NVM. Found it. Edge of Seventeen by hariboo. Was looking on FF.net and couldn't find it cause it was on AO3.