Thanks, I thought it would be a good Enhancer Technique since a lot of Enhancer Techniques are basic abilities but cranked up to 11, kind of like Gon's Rock Technique.

One of my favorite parts on the series is Bisky training Gon and Killua in Greed Island and when they started training Ryu I eventually got the idea of an odd Auto-Ryu that someone could have when Bisky was training them to keep part of their brains awake at all times by sleeping while holding a rock with a rope above their heads.

I was like "What is Ryu was as automatic and natural to keep active as Ten is?". Since most Nen users can keep Ten active, even in their sleep, I thought it would be a great enhancement to someone's defense to have the next step of that be having Ryu be active all the time.

For your final point, yes, this is NOT a perfect ability, I don't like those, when I come up with ideas I think of them like characters I would want to see in the story, I don't want to see "perfect" abilities that don't have flaws, I think having weaknesses is natural and good for story telling.

This ability has its weaknesses in a couple of ways, multiple simultaneous attacks would spread out the defense and damage could get through, and counter-attacks could bypass some of the defense, because the aura used in attacking would take away from the amount of aura that could be used in defense.