The Sergeant Major of the Marine Corps is selected by the Commandant of the Marine Corps to serve as his advisor and as the preeminent and highest ranking enlisted Marine with a protocol equivalency of a three-star general officer.

As with the other joint chiefs, the commandant is an administrative position and has no operational command authority over United States Marine Corps forces (this surprises me but I know virtually nothing about the military.)

I can't really tell what you are trying to ask, so I will answer what I think you are trying to ask. The senior enlisted advisor of each branch is the only enlisted person that holds an official protocol rank greater than their actual rank. The SEAC has a protocol rank behind all 4-stars at whatever event they are at. Besides that, the senior enlisted person at each command/installation has an unofficial (at least I have never seen anything official) protocol rank behind the deputy commander/executive officer for said command/installation. All of that goes with the fact though that those people do not hold military authority over the lowest second lieutenant (but said O1 better do as he is told).

Langenator said:

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Well, a good E-9 wouldn't actually tell that O-1 to do anything. He'd simply suggest/advise said O-1, and that O-1 would be wise to heed.

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As you say, the good ones know how to handle it without ever undercutting their officer's authority.