This is the risky one.
"Of course, of course. Tradition is an important part of comity, after all. I shall expect that when conducting matters of state my counterparts to do likewise, naturally."
And with that he is all sewn up to the compromise standards of the Protectorate. Promise bows again. To the gate.
"This can return you to your city, Lady Promise, before continuing on to bring His Majesty to our leaders. Suitable accommodations" as in appearances "can be maintained indefinitely."
The ship takes off, and starts flying south. Nilbog is seeming to enjoy himself, what with being less isolated than at any time in the last ten years.
Eventually the transport does drop Promise off at Brockton Bay and Nilbog at a gilded cage near the main headquarters. He is thoroughly impressed, especially with the enormous armchair sized for his puppet body. His last throne had been hacked together out of ordinary furniture. His captors keep him happy with frequent meetings with people he gets told are nobility, and consultations on issues of relations between states, some of which are even real. He continues to have no idea he's a prisoner, but the PRT gets to announce the victory it wanted.
Promise, meanwhile, makes sure to tell the Brockton Bay PRT that if they want to ask Nilbog to reconsider fighting Endbringers, Promise will need to deliver the request unless they want to risk the answer being "sure... wait... my powers aren't working". They'll forward that up appropriately, won't they?
Alexandria and the Chief Director have been annoyed at that having not already been included; Promise might end up unavailable or even unwilling by the time their diplomats convince Nilbog. But nearly everyone is more than satisfied with the almost perfect success against someone who used to get listed in the same breath as Endbringers.
"I didn't think anyone wanted it left to Nilbog's judgment whether something constituted a sufficient threat or when during the proceedings to start or what exactly to use his power on, and I couldn't work any of that specificity into the pretense."
The Chief Director, or someone speaking for her, replies to her email, "Does that mean we can't maintain the pretense past the next Endbringer attack? Any such change would have to be along the lines of saying that the tradition permits power use in emergencies at the request of the host, and from what you've previously expressed that might be more than you want to leave to our judgment."
Promise replies: "I'd probably say something about diplomatic traditions being suspended in the event of an emergency for foreign heads of state lending combat assistance, then not actually lift the order until he was on site and phrase the limits as tactical suggestions. At any rate, the pretense doesn't actually need to last now that he's not with his creatures; I'd sooner keep it if we can but it was mostly important to avoid problems with the unvassaled critters."
"He is more likely to cooperate if we do. Though I would prefer a solution less dependent on your permanent involvement, especially at such a detailed level as on-site tactics. That is unlikely to be the most effective use either of his powers or of yours. But we almost a month before the next Endbringer attack, and Nilbog has not even agreed to help yet."
"I can't directly master Endbringers and I'm not an efficient healer of people I haven't had some time to study first. If you have a better idea for things I can do besides direct otherwise-dangerous capes against them I'd be happy to reconsider my plans for assisting, but I don't have anything."
It's common knowledge that radiation is what kills anyone who gets too close to Behemoth.
"Well, I can study up on the radiation and see if I can develop a spell, but it sounds awkward to test. I can give orders while studying injured people, though."
"What do you anticipate ordering him for, other than the easily done ahead of time things he might not care about such as collateral damage to allied forces?"
"What things he's allowed to turn into creatures. What he should do with the creatures afterwards, especially since at least some of them are people."
"Both of those are also easily proscribed in advance. If he makes nothing more intelligent than a dog, and never out of anything human, you could merely direct him against appropriate targets."
"I'll see if I can come up with some appropriate order sets and formatting for them in plenty of time for the next attack, then."
Her force field generator will be completed in a matter of days.
In her copious spare time she does research and eventually comes up with an order set in which she informs/"reminds" Nilbog that his majesty is invited to join battle against the Endbringers, which would suspend his (ever so gracious) agreement not to use his powers, though certainly everyone understands that (in spite of his obvious diplomatic immunity; isn't that an interesting concept?) there is no call to make other heads of state feel inadequate to their task of protecting their people by using those people as raw materials, and also it would desperately confuse any questions of citizenship if he created any creatures smarter than dogs outside of his own realm.
When she reads it, it turns out to be detailed information on some of Brockton Bay's villains.
Cape name: Kaiser. Power: creates metal objects from any solid surface. Leader of the Empire Eighty-Eight, a gang dedicated to the proposition that someone's value as a person can be measured by the whiteness of their skin. Directly or indirectly responsible for quite a lot of crimes in support of driving the undesirables out of the city. (A selection is listed, along with his involvement. Mostly assaults and robberies, some murders. The drug dealing is emphasized less, since crimes that are nonexistent in Fairyland might be less likely to offend Promise.) But, for fairness purposes, Kaiser himself does not agree with this goal and is only in it for the power. With him gone, there would be no single obvious successor and the Empire would fracture. Real name: Max Anders.
Krieg, James Fliescher. Power, known crimes, position in the Empire, expected consequences of his removal.
If she decides to continue reading, there is similar information for all the rest of Empire 88's capes, over twenty of them. Purity, Hookwolf, and on down the list from most to least important.
She emails the Director:
"I got an anonymous message from someone with real names of Empire 88 capes. I didn't read the whole thing, but I have two now."