Hey guys, I had an idea. During the first fight Ichigo had with Kenpachi Zaraki, Kenpachi was able to avoid taking any damage and inflict damage on Ichigo due to his high Reiatsu level. So I was thinking that perhaps Shinigami as a whole could possibly attain this augment as well, as it would become something comparable to Hierro or Blut Vene.

That was something Kenpachi alone was able to attain. It's an ability that he only showed that one time during a fight with a weaker Shinigami. And he explained that Ichigo was simply not putting enough strength into his Reiatsu. After he did that, he was able to fight with him on equal terms.

The Zaraki vs. Ichi scene stands in contrast to the Zaraki vs. Nnoitra scene where it never depended on the Reiatsu strength of Reiatsu, but simply on the physical strength Zaraki didn't put in his strikes when he couldn't cut him. Hierro is a natural ability for all Arrancar, albeit shining insignificantly in some. All Arrancar have it. Next to that, Shinigami have the gigantic list of Kido, two basic release forms and a lot of augments. I don't really see why they would need an additional defensive ability, especially when it's one just about the strength of somebody's Reiatsu. That technique would really apply to any character of any race as long as he or she plays him or herself Zaraki-esque. Basically you just need to say "My character has this big load of Reiatsu on his/her back! It's basically the same amount Zaraki!" and you can powerplay yourself in front of Officer-ranked characters.

I see, thanks for explaining. And yeah, Shinigami do have all those things, I was just thinking of a more straight-up comparison than equivalents. But I see your point, adding something else would be overkill.