User blog comment:Xilinoc/Ch. 562 - THE VILLAIN 2 (Mask De Masculine is a Mexican luchador in a German army)/@comment-5147109-20131219001055

The way I see it for Renji is based on the Royal Guards we know about we have the following:

Tenjiro (Master of healing) - He fixed up Renji's body back to full strength

Kirio - (Master of Reiatsu) - She fed him that food that was shown to dramatically increase Renji and Ichigo's already formidable Reiatsu.

Oestsu - (Master of Zanpakutos) - He fixed up Renji's Zanpakuto and I'm sure after all of that Renji's bond with Zabimaru is stronger than ever which means he can draw strength from it.

Sanjumaru - (Master of the cloth so to speak) - She hooked him up with the clothing that he currently has which is currently unknown what benefits it provides but I'm sure that they definitely help out in his battle.

Ichibei - (Not sure what his specialty is but if I had to guess based on what we've seen it is likely he is the master of combat) - After training with him, based on what was said about Ichigo's power stabilizing to the point where they called him a true Shinigami, it is likely that Renji's power stabilized and strengthened in a similar way because ,much like Ichigo, Renji throughout the series had largely been training in a similar fashion, with the exception of the 17 month duration after the defeat of Aizen where we saw Renji's power already increase significantly further than what he had previously been at, add his training in the Royal Realm and the fact that Renji is a Bankai user it is likely that Renji is now at the same level as the captains and possibly higher than some. My final statement regarding this is that it is well known that a cool head in the heat of battle can tip the odds in one's favor, and we have all seen based on this latest chapter that while Mask is all hotheaded Renji is staying calm and collected through the whole thing, he is carefully calculating his moves and not making any rash decisions, combine all of this together and you have one bad ass Shinigami ready to throw down.