A suggestion. But have no idea of practicality as of yet.

Since we have reiatsu perception already, why not add reiatsu strength? To measure the strength of someone's spiritual pressure. Different effects of it can be created as well, of course only if there is a considerable gap in the amount of it.

For example, Nanao was completely paralyzed by Yamamoto by just looking at her in the eye. That was the effect of his spiritual pressure. Why no we add such effects here as well. The ability to strike fear, paralyze and, if there is a large enough gap, even kill the opponent just by exerting the spiritual pressure.

This idea could be worked on and refined if necessary.

The primary reason behind this lack of is because it's so vague and over-powered. We have a similar, 'hidden' way of measuring, by comparing Tiers and ranks, though the latter is not always reliable. A Veteran Captain has more spiritual pressure than a normal Captain, though.

As I said, we could refine it from vague to being defined. We can tone it down to take away the over-powered state as well. Maybe even take away the ability to kill with it.

I never did like that it could kill. I think the extent of it should be that, to an EXTREMELY weak person, it would paralyze them. But a Leiutenant should NOT be paralyzed by, say the Captain Commander's Reaitsu. It should also have a visible effect on those weaker. Like for example. When Orihime and Quincy Man (I always forget his name) felt Ulqy's Segunda's Reiatsu, they described it as feeling as if the Ocean was crashing down upon them with it's entire weight.

That's the basic idea. The biggest effect would be paralysis. For that to happen, maybe a gap of three tiers should exist as minimum? Maybe some other effect maybe added as debuff or stuff for shorter gap?