I like the sound of 'Sergeant-at-Arms' myself. But Discworld probably has something to do with that.
Thanks for spoilering that picture! Also, yeah, while I like Discworld, unfortunately, Sergeant-at-Arms has a nobility/knightly thing going for it, and while -everyone in NERV would disagree with me-, NERV is not a monarchy, duchy, or barony.
Anyway, I went with SFC, as that's the first grade of Sergeant that can be an NCOIC.
EDIT:
I mean, what grade of sergeant doesn't matter much, ultimately. He's still a NCO leading a section, one of the the primary divisions of NERV. Just give him a commission, Gendo!
There's a reason you don't put officers in charge of training soldiers. He's a Drill Instructor in charge of their training, not the bean-counter responsible for making sure all their simulators came in and are the right model. That's Gendo!
Also, what grade of Sergeant he is -does- matter, as you can (and do) have NCOIC, or 'Non-Commissioned Officer In Charge'. This is basically a soldier running a section -like- a soldier, rather than a REMF running a section like a REMF while acting like he's a soldier.
In short, the officers are supposed to provide strategy, while NCOs are supposed to provide tactics, and sections or bases run by these two differing (but similar) schools of thought can be wildly different. You do -not- want a long-term strategist trying to get results out of your soldiers -now-. The build-up would be too slow, too gradual. Nor, however, do you want a short-term tactician training your soldiers for an engagement that's eighteen months away. You'd burn them out -way- too damn fast.
*coughs* ....Sorry, is my work-for-a-living-bias showing again?