Originally posted by Astner
I missed this quote before.Renji Abarai was incredibly powerful to begin with. He was the first lieutenant to attain bankai and when he did he managed to get Byakuya Kuchiki to his knees.
Renji's goal has always been to surpass Byakuya. Up until now. Now his goal is to be able to defeat Aizen. The new standard may be more motivating, and that's why his powers increased so drastically. But when you zoom out you realize that it's not so unbelievable.
Renji trained with Ichigo to attain bankai, and received it before him. This shows that Renji is a quick learner as long as he's motivated.
Ichigo trained for two years to master the final getsuga tenshō and Renji trained for one year and five months to reach his current state of power.
Close, but not entirely true.
Renji trained for 10 years, most likely, because he didn't use the "special" cheater way. He had to work on materializing his Zanpakuto and he had already done so before Ichigo started his thing.
In fact, only Urahara had succeeded prior to Ichigo as seen here:
http://www.mangareader.net/94-586-20/bleach/chapter-132.html
So Renji was working on activating his Bankai more than...a few seconds? We don't know how far along he was in getting his bankai or if it was just simply maintaining it. However, we do know that it was deemed incomplete and that more training was required as stated by Kuchiki.
We also get further confirmation that he is almost to the point of bankai release:
http://www.mangareader.net/94-587-15/bleach/chapter-133.html
So he was working on it quite a bit before the start of the series...no cheater way to get it faster.
Addtionally, he may not have been the first lieutenant to achieve bankai of the current generation: Ikakku was his superior and helped train Renji so it may be more likely that Ikakku has achieved his for quite some time. Lastly, we know from his exchange with Renji (when Renji was in the 11th division) that he had a Bankai for quite some time...years maybe. This was before Renji got his.
Iba may have also achieved his bankai. He's Ikkaku's equal in most ways and may even be his Kido superior.