Talk:Narberal Gamma/Abilities and Powers/@comment-34598988-20180703231858/@comment-45.56.46.26-20180704135130

It is established in Vol 2.

"The two of them had already discussed their plans for emergencies. Narberal would cast magic of the 5th tier if things came to that. And if that did not work either, Ainz would shed his armor and take the situation a little seriously."

For the most part, it seems that the story is that Nabe is skilled with the sword as well as with magic, thus plausibly reducing her casting ability. Also, they maintain a setting where she is less powerful than Momon (of course, since Evileye can assess that Momon would be above level 66, it's not like Nabe can seem more powerful even by going all out).

So while it is unlikely that Ainz changed the order to use magic up to the 5th tier if necessary to prevent Ainz from having to reveal himself, there is no real reason to change the setting of it being a hidden trump card. In fact, now that Momon uses [Perfect Warrior] so often, there is far less chance of 5th tier magic being useful against something he can't handle.

Momon also has the established setting of refusing to go all-out against strong enemies if it would cause a lot of collateral damage. So even in a true emergency, retreating wouldn't break character.