He acquires the vervain and pencils a few runes on the floor around Promise. He draws a simple circle around her chair, draws a line of runes from it to a spot near him, and draws another simple circle from that spot around himself. He begins his lengthy Germanic healing chant. Glowing eventually occurs in Promise's heart and arm, and the chant ceases. "Well, looks like that worked. Congratulations, fairies are healable."
"Your kinds of fairies can die?" she asks, peeling up the clay to look at her fixed arm.
"I wouldn't be pleased about it if you stabbed me but I couldn't die."
Mothers and Queens and a tribe of fucking cobbs.
"That's... horrifying. And very disappointing, given my fond dream of someday watching our boss suffer an agonizing death. I'm guessing that if a fairy were to be, say, crushed under a very large rock, or perhaps beaten into a gritty paste, his vassals would not in fact be freed and he would eventually come back and be very unhappy?"
Hope lost, Ari elects to look on the bright side. There is no bright side, so he elects instead to ignore the issue entirely and move on to doing his job. He erases his previous work, then draws a circle around himself, puts down a single rune, and holds the cup of Promise's blood in fromt of him. "If you'd like to watch the fireworks, feel free. They will be very pretty, but there's a chance they might be eye-searingly bright."
"Where will the point of origin of the brightness be? I can protect my eyes if I know in advance."
"It'll come out of the cup. Might reach a bit farther than that if it's too strong, though."
Promise nods and peers at the cup, then tilts her head and says, "Go ahead."
The bowl in his hands turns into something that could be described as a "Skittles nuke".
It is so, so bright. It is so, so colorful. The flame hits the edge of his circle and splashes back around until it practically fills up the cylindrical ward. Ari closes his eyes a fraction of a second after the spell goes off, but he still feels light hammering on his retinas through the lids. But the duration is the same, and after four accelerated heartbeats the light vanishes. Ari can't really tell, because everything is grey.
Very, very carefully, he sits down and waits for his vision to return. "I am not dead!" he calls to Promise, to clarify.
"Well," she says, "that's good, because my idea will only work if you're alive. Unfortunately, it can also only work if you're willing to trust me."
"What? Idea? What idea? What's this about ideas? Can you hand me some vervain, I need to fix my eyes, we can talk about ideas after I stop being blind."
Ari blinks a few times. "Much obliged. Would've been pretty hard to cure myself while I was still blind. What's this about ideas?"
"It is possible for two people to be vassals of each other, under the right conditions. New orders from any master supersede previous ones from any master. He hasn't had you long enough to close a lot of loopholes, and I have one he hasn't noticed that I've been saving. For whatever it's worth, my idea requires me to trust you a lot more than the other way around, because it will only work if you vassalize me first."
Ari considers this plan. He sees no flaws. He considers reasons not to trust Promise. She's a vassal; could this be a plot from the Creep? What does the Creep stand to gain, he could literally just ask "how do you feel about me" and have done. Could this be a plot to curry his favor or something? Doesn't make sense, he already likes her and making an extraordinary request could fuck up her position. And it really helps him trust her that she's the one who's going to be vassalled first. That's a good thing, he likes that. He's going to trust her.
"This sounds like an excellent plan. I'm somewhat in love with your plan, I'd like to marry it and then use it to get us the hell out of here. What should I do?"
"I need to know how much leeway you have, first - don't say it if he hasn't, but I assume he's forbidden you to say your name?"
"He forbade me to say it to anyone else. I'm pretty sure that can be circumvented by recording me saying it to myself, though. If not just talking to myself loudly while you're in the room. He's really not as good at loophole-mongering as I'd expect, my mother would be horrified."
Promise shakes her head. "He thinks of things in bits and pieces over longer periods of time. I'd have got out long ago but the master who gave me to him was much better at it and Master didn't directly rescind any of his orders. Okay. So you can say it to yourself, or maybe say it backwards or something. But I'm forbidden to give any enforced orders - holdover from long ago - so first I need to eat some of your mortal food, please tell me you have some, there are alternatives if you don't but they're less pleasant. And then you rescind my orders and then you tell me your name and I rescind yours and we get out of here. I know where you can find a gate to the mortal world."
"...I've got herbs? They're not exactly food, but I can certainly feed them to you. Ooh, actually, I think I've got a packet of beef jerky in my bag. Forgot about that." He rummages and comes up with a sad-looking plastic bag containing a single lonely unit of jerky. "Would this work?"
"Presumably. As long as it won't completely incapacitate me I'll eat whatever will envassalize me, anyway, and that it will definitely do. Can you feed me or did he catch that?"
He stops short. "Anything involving food. Goddammit."
Promise shrugs and seizes the bag out of his hand and pops the jerky into her mouth and chews. "Eugh," she mutters, but she swallows. And looks at Ari expectantly.
"Oh, that... works? Okay," Ari says. Feeling around for some indication that it worked, he intones, "I rescind all commands placed on you, by my right as your... master? I guess? Co-conspirator? Buddy?"