I was just going to introduce a background OC, when this world mechanic head-canon appeared and bit me on the backside. I've probably been reading too many HP/KHR fics, but it still fits and I'm keeping it.
Mokichi Omori was a good kid. He was also a good shinobi. He didn't look it, with the big glasses and the short tousled hair that framed a round, babyish face with long eyelashes and clean skin. He looked soft, weak, fodder-grade. To a Suna Jonin or Chunin, however, he looked dangerous. Because in this world, you couldn't afford to look soft unless you had serious skills.
In terms of shinobi-related accomplishments, his main skill was underestimation. His signature weapon were two small tessen, which contradicted his earth affinity. Enemies would expect wind techniques, only to find that he used them in the more traditional courtesan assassin manner; those who attacked would find that the protruding points of the spokes were laced with a variety of poisons. Speaking of poison, he was also a skilled iryo-nin. Nowhere near Tsunade's skill but his multi-tasking made him something else;he could patch you up with only one hand while successfully parrying a storm of various projectiles with the other. His only bad habit was that he could be very vindictive. That led to the rather unsettling interrogation scene where he broke every single bone in each of his victim's arms, while naming them. He was a good shinobi.
To Baki and several others, he was 'a good kid'. Because he was only a Genin, in the midst of all the Chunin and Jonin. He kept turning down promotion, because when people heard his rank, they underestimated him. He was the 'baby' of his peer group, and not only in rank; he was the youngest, with three years between him and Toju, the next youngest. That made Mokichi eight years younger than Baki. They looked out for each other, the lot of them, because this world was a cruel place but you needed someone to trust; especially when the Third Shinobi War began. Mokichi was there when Urayama was poisoned by Tsunade, he was there alongside Shima when they collapsed the ground beneath a platoon of Kumo shinobi, he was there when Ikoi needed extraction from her explosive-planting mission, he was there to back up a group of cornered Suna couriers, he was there when Toju needed a mercy killing from the agony of a crushed pelvis, he was there when Baki led a risky mission to the borders.
He was always there for them, with whirling tessen and a wry smirk and a healing jutsu.
So when he went missing on a patrol mission, they were there.
They found him, Baki slicing his signature Futon jutsu through the stomach of the first Uchiha and Urayama snicked the head of the one holding the genjutsu from her shoulders with razor wire. Shima and Ikoi took care of the rest while Otoe grabbed Mokichi and high-tailed it.
When Baki and Urayama regrouped with the rest at their designated fall-back point, Otoe had already released the genjutsu. He was shaking uncontrollably, pupils blown so wide his eyes were almost all black.
They didn't have the luxury of therapy in this war. Once he had been checked that he hadn't divulged anything, he had two days leave. It wasn't until a week after the genjutsu that he felt comfortable enough to talk, having been using hand-signs instead of vocalising. Apparently the genjutsu had involved centipedes and he didn't feel comfortable opening his mouth. It was during this period that Baki realised Mokichi was Resonated with him.
This, he had not anticipated. If it weren't for the fact that Baki already registered Mokichi as His, he would have felt more guilty about not Reciprocating. He told the rest of the group his discovery and was floored when they nodded and said they could see how it came about; Baki might not be the most approachable, but competency, seniority, the care he had for each of them must have attracted Mokichi. Who as far as they knew(and they knew a lot about him), didn't have any other Resonated, unlike them.
The end result was that Mokichi was practically fused to Baki throughout all the free time he had during the recovery period. Baki found a new appreciation for having a Resonated who had no qualms acting on their instincts, and began to feel a little ashamed that he didn't seem to Reciprocate. Unlike the Resonance he had with Rasa.
He wondered why Rasa still Resonated with him, despite Baki choosing and succeeding in breaking his Reciprocation with the implacable Kazekage(then-Candidate) years ago. Rasa had noticed; of course he did. But Rasa had had Baki still keep his title of Kaze no Ken. Really; it wasn't obvious? Rasa had blatantly stated that Baki was his right hand, his arm of power, to all and sundry. It meant that Baki could be an Interim Kazekage should the need ever arise, but to the two men it was Rasa marking out his territory; Baki was Rasa's, no matter if it wasn't a Reciprocated Resonance.
The man was a pissy little bastard when the mood took him.
Baki suspected that even without the trauma, Mokichi wouldn't mind being as demonstrative as he was at the moment. Baki actually stayed at the younger man's place several times, usually sharing the bed. Nothing sexual about it; just two chakra systems balancing each other with their proximity and skin contact.
Rasa would never do that, Baki knew. The only Resonating touches he and Baki had shared were small ones merely to the hands and face and even then Baki had only touched Rasa's face once. He had been drugged and shivering with fever-bright eyes and Baki had flown to his distress with little care for other duties. He had touched the older man's face, merely reaching out to trace the chakra paths and some deeply ingrained instinct had seized Rasa's consciousness to break Baki's arm. That would not have phased Baki, had it not been for the look of violation and self-loathing in Rasa's eyes.
It wasn't the first indication Baki had that something inside Rasa was broken, but it was the first one that hurt.
When Rasa hurriedly took up the mantle of Kazekage, he made the choice to wear the veil and look Baki in the eyes while wearing it. Baki once would sit behind Rasa's shoulder, but now he had to deliver his reports with a rattan screen between them and let guards hand things to Rasa for him. It was the knowledge that Rasa felt better off without him caring that made Baki reach deep inside himself and sever the bond.
Then Rasa chose not to let him go. Baki was still his right hand.
Baki's chakra registered Rasa merely as a powerful shinobi who Baki knew. With the Resonance broken on the younger man's end, Rasa no longer felt RightSafePowerHome to Baki as he once had. He still let Rasa touch him, he wasn't cruel enough to deprive the older man Resonating touches, but now it was his human decency and respect and devotion to his Kage that made him do it rather than his own chakra's need.
What creeped him out the most was the fact there was no pain or wrongness once the bond was gone. His chakra was no different, it had simply reclassified Rasa and the man's new designation meant it would not react in the same way. Where once their chakras would automatically balance and soothe, it was now a one-sided effort. Baki neither gained nor lost anything, he was neutral now. While Rasa's chakra would still balance when they were close, it would never be quite as long-lasting; it was how Unreciprocated Resonation worked.
Baki was quite happy for Mokichi to Resonate with him. They were still on the same team every now and again and once the trauma began to subside, that was all they needed.
Baki might not Reciprocate Mokichi's Resonance bond, but he was a Possessive. That meant Mokichi was His. A Possessive bond was close enough to a Resonance for other shinobi to acknowledge. Baki and Rasa had been (and still were, technically, but Baki suspected Rasa was Possessive towards him now)Equal and Urayama was Possessive of Baki.
As the oldest, Urayama was Possessive of the whole group with the exception of Mokichi and Ikoi. Baki was Possessive of Mokichi while Ikoi and Urayama had a Reciprocated Resonance plus a sexual relationship.
It felt unusual to Baki to be Possessive, but it felt right. While Mokichi's chakra balanced, Baki's called out MineFamilyMineProtectMine. It didn't really change anything in a sense. Mokichi got no special privileges, he wasn't exempt from missions and got no extra pay. As Mokichi's Resonator, Baki got the same rights as blood-family; Mokichi having no blood-family, Baki was the designated next of kin in all official documents.
That was it.
They still drove each other up the wall on certain things, liked different things and at times flat out hated each other, but Mokichi still needed Baki and Baki still felt the urge to protect Mokichi.
Suna shinobi do have their bonds and 'precious people', they simply have a more elaborate system of classification. It makes more sense and helps to prevent other shinobi overstepping boundaries and potentially getting hurt. They don't understand why Konoha shinobi are so vague about something so important, but they respect that the four-man Genin cell set-up promotes Resonance on a broader spectrum. Suna sticks to a tutoring system to form Resonances quicker and stronger.
Kiri is looked down upon in particular by Suna, because the infamous graduation exam made students forcibly break whatever Resonances they had with fellow students and teachers. This process inevitably led to Kiri shinobi being bloodthirsty, often killing their comrades and having little personal loyalty to their Village. It's why Kiri had such a high output of nukenin.
For Reference:
Resonance
A bond formed by chakras that balance each other out.
Reciprocated
The Resonance is mutual. E.g. Person A's chakra is balanced by Person B's chakra, while Person B's chakra is balanced by Person A's chakra.
Unreciprocated
The Resonance is not mutual. E.g. Person A's chakra is balanced by Person B's chakra, while Person B's chakra is neutral/unresponsive to Person A's chakra. Sentence use: Person B is a Resonator, while Person A is Resonated.
Resonances have to be formed unconsciously the first time, but can be consciously broken. The Resonance can be reformed, but must be done consciously.
A person can break their own Resonance with no side effects. Resonance's can be broken by a third party through torture, but usually restore quickly upon removal from the scenario.
Shinobi with a Resonator are 86% less likely to turn to substance abuse than shinobi without.
Shinobi who are closely attuned to animals, whether summons or nin-animals, are more likely to respond to threats to their Resonated/Shielded/Equal with force.
Possessive
One person feels a sense of territorial responsibility towards another. Resonation is not needed on either end, but can be included. Possessives are often Unreciprocating Resonators. The Possessive is often stronger or older than the Shielded, though there are several exceptions.
Shielded
A person is the territorial responsibility of another. Resonation is not needed on either end, but can be included.
Equal
Neither Possessive nor Shielded. The majority of these shinobi have a Reciprocated Resonance.
