User blog comment:Godisme/Bad Blood Exhaust/@comment-1837917-20110923055056

I think that when Renji says he's been training to 'be able to fight Aizen', he's implying that the Soul Society didn't simply forget it was brought to the brink of destruction, and the Gotei 13 have actually improved so nothing like that will happen again. Bringing Aizen back does nothing for the plot.