Its pretty much exactly as it sounds.
Its a psychometry pattern which tracks the two parties' behaviors to ensure they keep their part of the bargain. If the pattern senses a violation, it will mark the violator, for what amounts to execution.
After the invasion, the demons established a collaborative 'contract' system with the humans. Why kill each other when you can profit instead?
Enter: the devil's bargain. As Egil understood it, its essentially a bounty system. You establish a magical contract with a demon and you gotta meet your requirements. If you don't, you get a bounty place on your head. You can technically pay it off yourself, but exceeds what kings are normally capable of.
This option, as far as the stories go, exists because the 'oath breaker' might have unique access to something the 'oath hunter' factions want, but would never agree to share / give up under normal agreements. This obviously implies some sort of 'entrapment' on the oath hunters' part, but nobody is really complaining.
The normal course of enforcement are the bounty hunters... ALL of them. The bounties paid to hunters are lower than the price that the oath breaker would need to pay, but also still pretty high, even for small bounties.
Really, the core of the idea is: you break a bargain, and the oath hunters want you dead. All oath breakers have brands that show up on their auras, so *everything* with an open third eye will see it.
Then there are the specialists: on top everyone in the know, seeing the temptation of a big payout that could change their circumstances overnight, there are also actual, dedicated hunters. These are organized teams that make their living off bounties. Where bystanders might hesitate to kill an oath breaker, the specialists won't.
To Egil's knowledge: pretty much no one has survived more than a year or two with this type of bounty.
Entering into a bargain pretty much guarantees the trust of all involved, because the stakes are so high.
Egil pushed his way through a set of the library's exit doors, and approached the three demons; none of which he recognized. Nothing distinguishing them either. Lame.
There's no way Lindir came down here without expressing his intent. These demon's had to know who Lindir was looking for. "Where's Curie and the incubus Lindir seemed so fond of?"
The three exchanged puzzled looks. "Uh, he dismissed both of them."
"They're ok, right? Alive?" Funny thing human society never reconciled: not even dead demons went back to the entropic layer. Its not an afterlife.
"Why do you care?"
Ehhh... let's sow a seed. "They seemed nice. I was impressed with their abilities." It was a half assed effort, but Egil was already getting bored with the Lindir encounter.
"They're fine, just no longer in his service."
...traded like a pack of smokes...
Egil wasn't interested in recruiting them. Curie was stand-offish with the church, which was definitely not something he needed. The incubus, he knew even less about, and probably had some leftover baggage from Lindir.
"Shame. I liked them." ...meh... "Ok, down to business: I need a bargain, or Lindir's getting executed." The oath hunters only concern themselves with the bargain, and not the circumstances that birthed it.
The incubi drew their various weapons.
Wanna posture? Egil bobbed to the left ...outcome 2... he was now standing a foot to the left. Bob to the right ...outcome 3... he was now standing a foot to the right of where he was initially. ...outcome 4... he now stood where he was originally. From the outside, it looked like he flash stepped to multiple locations simultaneously.
"What the fuck?" The opposing side murmured. "He's not the summoner?"
"Fucking coward won't even come out to meet us in person."
Interesting! It didn't cross Egil's mind that the mask's ability would create doubt that he's human. This could be useful. "It would be a shame if this ends in avoidable bloodshed; and I will totally give the execution order during our fight."
"What kind of demon are you?" One of them asked.
"The kind who is demanding a bargain." Egil responded.
"Ok, what do you want?"
Time for a 'boiler plate' agreement. There's a frightening amount of literature on this topic. After so many early disputes, and miscarriages of enforcement, both humans of the guild, and demons essentially 'lawyered up.'
One of the things to come out of this was a set of standard definitions for various activities, both legal and wildly illegal by human standards. These definitions were meant to help facilitate rapid verbal agreements.
"I want the generic non-disclosure agreement about all events that have happened on this date." The 'generic non-disclosure' basically meant none of them could talk about the agreement's details. They can, however, say they have an agreement, which prevents them from saying more. They can't say who the agreement is with. It lasts for a period of a year and a day.
Egil continued: "In return, I promise to leave Lindir in the red light district in the standard recoverable state as defined for prisoners." The 'standard' came with a ton of protections on both sides. The short story is: the captive needs to be delivered, with all their parts attached; any exceptions need to be stated ahead of time, as part of the bargain, or it won't form.
The captive must have a reasonable expectation of survival, before, during, and for a little while after their recovery. Some exceptions exist for cases like catching pneumonia while waiting for recovery.
The incubi agreed, and left.
This still wasn't very reassuring though. Egil looked back at the sparse library defenders. If someone really wants to take this place, there still isn't a lot stopping them.
