For @Valandhir - This is an idea that occurred to me a couple of days ago, not directly related to any of our current timelines, but a lot of small details have filtered in.
Canon events happened as per canon. Kíli died in the BoFA, Boromir died at Amon Hen. This happens after.
Once there was a man named Boromir, son of Denethor, who went on a journey, joined a Fellowship, and died. It was only after he died that he found his existence had just begun.
The grim guardian warrior he met after death was not unexpected, but meeting the Great Smith, Aulë, at the same time was. Aulë had an offer for him, an invitation to his halls, instead of the unknown beyond that all Men when on to.
It was a strange offer, to Boromir's mind, but one that, given some moments to consider, he liked the sound of. Death was said to be a gift to Men, but the influence of Dark forces that made Men see it as something to fear had never been fully shake off, so going to some afterlife far more sure than the unknown beyond the World felt more reassuring.
Mayhap, Boromir thought to himself, he should have recalled the great legends about the Powers, it may have reminded him that Lord Aulë was always told to be the father of Dwarven-kind, but as he gave himself time to adjust, he found he liked their manner - rough and tumble though they can be - enough to not regret his choice. They were honourable too, something that appealed to his sensibilities.
One dwarf however kept drawing his curiosity, one who called himself Kíli, though he would get called any number of other names by various others - Askíl, Finrir, Tiórvi, Thoraine (that one Boromir at first confused with Thorin, the name of the dwarf Kíli called "Uncle" though Boromir had also heard it said that he was Kíli's father). It puzzled Boromir, but he did not feel it was his place to ask.
Time and again, Boromir found himself being drawn to Kíli, and not thinking too deeply into it, set about getting to know him, finding him to be a good soul with a kindly and cheerful manner. He seemed to avoid questions about the other names he got called, especially when his brother (so Boromir had ascertained), a dwarf by the name of Frérin, kept using 'Askíl'. Frérin's continued use of the name got him into more arguments with Kíli's blond brother, Fíli, than it ever did with Kíli himself. The whole matter was a bit confusing to Boromir, but then, he thought, he and Faramir had not had another sibling to fight over, and though their father showed a tendency to favouritism, it had not caused disputes between them, but in fact drove them closer together.
It was due to the arguments though that Boromir met the other Man who resided in these Halls. Talion was Frérin's partner (the beliefs of Gondor against romantic liaisons between men already being eroded in Boromir's mind due to the high frequency of all-male pairs amongst Dwarves), though he often stayed away from the heavily frequented gathering areas. Though his manner was somewhat different to Gondorian culture, Boromir did find it comforting to have another Man who could help him understand better.
"There are a few great souls Lord Mahal has sent back to the living world, to live another life." Talion explained. "Askíl was one such soul, one Lord Mahal called to be reborn more than most. He was Frérin's brother, but was also Fíli's, though centuries separate those lives."
Talion's words certainly explained some of what Boromir saw going on around Kíli, why he gained so much attention from random dwarves, and why he tried to avoid being seen around too much, letting his close family shield him from unwanted attention. Boromir however was one person they seemed to let in, and for that he was grateful. It gave him the chance to spend time with Kíli, getting to know and understand him better.
Kíli was... everything Boromir could imagine liking. No, Boromir started to realise, everything he wished for in someone *more* than a friend. It was something that Boromir initially thought to keep to himself, but of all the people to pull him up about it, it was Thorin Oakenshield (a name Boromir had to admit was slightly familiar, something he heard on the quest to destroy the Ring) who told him, in no uncertain terms, to stop playing with Kíli's affections.
That in itself was news to Boromir as well, but after Thorin's words he started to see how Kíli's would be more open to him than to any other beyond his two closest brothers (some of his other lives had brothers in them as well, but some of them, particularly Aurvang's family, treated Kíli ill, rousing Fíli and Frérin's ire) and found himself responding to it with a joy he never thought he would find again. To have Kíli return that? The bliss was beyond anything he had ever felt.
Kíli's close family approved, Fíli smirked, Frérin grinned, Thorin, Ida, Dís, Dári, and a handful of others from other lifetimes smiled in varying contentment and good cheer. Talion told Boromir that all of those close to Kíli had long worried for him, as he had never found his *One* in any of his lives. On learning the depth of meaning behind the concept of someone's *One* that Dwarrow believed in, Boromir had his doubts, but would not let them cause any hurt to Kíli.
The gentle progress of their closeness... it became a time of deep happiness for Boromir, to find someone he cared about so dearly, someone he could love. It seemed a small irony to him that he would only find love like this after his death (not that he had not loved those partners he had in life, but that what he felt now felt so much stronger).
Things came to a point when Lord Mahal declared it Durin's Day, a day Boromir knew was an important dwarven celebration (in fact it was one of the small collection of facts he knew from before his death, having heard it mentioned by Gimli somewhere along the way). Contrary to the attitude of most other dwarves, the reaction of the extended family of Kíli was strangely conflicted.Oh, on the front they seemed to be glad of the celebration, but at the same time they closed ranks, their guard around Kíli growing deeper, protecting him from random passers-by who seemed to feel a need to approach him more now than ever. The only ones they let pass without a word were those Boromir had learned were members of Thorin's Company (it had surprised him to realise these were some of the dwarves Gimli's father had traveled with to reclaim the Mountain Home, and to know Kíli was one of the fallen cousins Gimli had spoken of), the closer members of Kíli's previous lives (ones like Frérin and Talion, Tiórvi's son and heir, Finrir's son, fallen at the same time as he, when the balrog came up from the Deeps of Moria, and of course none would presume to refuse Mahal, who for whatever reason sought Kíli out several times.
The truth of why this reaction came about was fully answered on Durin's Day, when Mahal called for Durin to stand at his side and it was Kíli who stepped up to stand at the Great Smith's side.
"He has never been overly fond of the way people treat him." Frérin told Boromir when the question came up of Kíli's avoidance and how the family protected him. "In his first life much of what would become dwarven tradition was just starting to form. Even in my time much of the later traditions were not so ridged as they became." A laugh bubbled up in Frérin, "The first thing he did when he arrived here after his life as Askíl was to punch me in the nose and yell at me for leaving him to take the throne and have to bear the name of Durin the Second. Called me all sorts of a fool for getting myself killed, Talion... and leaving him to raise Hurán." Frérin sighed.
After Durin's Day, Boromir had some concern about being so close to such a respected figure, but it was Kíli himself that put a stop to that, pulling him into the forge hidden deep in the quarters his family lived in. "I won't stand for you treating me like something to be put on a pedestal, Targunyál. I *can't* live with that... not from you of all people." The sadness and need in Kíli's eyes as he said that was the final straw for Boromir, as he pulled Kíli tightly into his arms and kissed him, assuring him without words that he would not distance himself from Kíli, not let his status as Durin separate them.
The change that brought... If Boromir had thought he was happy before, when their relationship was just starting to form, what he and Kíli had now was ecstatic. They quickly found their way into intimacy and Boromir could only think that if Kíli had not died in the Battle of Dale, they might have met and fallen in love in the living world.
Boromir and Kíli would have the formal recognition of their bonding presided over by Mahal himself, something that would silence a few problematic nay-sayers, such as Aurvang's father, who disapproved of Kíli, claiming he could not believe Durin could be such an unworthy character, and Dáin Ironfoot, the king who ruled Erebor before Boromir's passing, having come to the Halls not long after Boromir did. Not that such souls could get very far with their attitudes, Mahal disapproved of their opinions towards Kíli and not even they would dare stand against the Father of Dwarf-kind.
Boromir had no measure for the time that passed after their bonding, only that he knew that having Kíli as his own was true bliss and gave his soul a sense of peace he had never felt before, a peace from feeling whole and complete, of knowing Kíli was his One. But that would come to change, when one day Mahal came to speak to them privately.
"When I sent you out, my son, to live your last life, I had hoped to see you live longer and eventually lead your people back to Khazad-dûm, once the monster that haunted it's halls was felled." the Vala spoke in subdued tones. "That destiny was subverted when your life was cut short, and the city never reclaimed."
"What would you ask of us then Father?" Kíli asked in a tone that seemed to speak of all his seven lives.
"I would ask if you would consent to live one more time, to complete the destiny you were prevented from following and bring my children back to Khazad-dûm, before their time in the World is over."
Kíli seemed unsure and a bit daunted by this request, and Boromir understood why, as he now knew the depths of Kíli's heart and knew how painful all his lives had been. To go back and possibly face more pain? Kíli looked up at him, a fear in his eyes of being separated from Boromir.
"Do not fear, my son." Mahal spoke again, drawing Kíli's attention back to him. "If you do consent - and I will not force you to do this - it is not you alone who will return to the living world," the Vala's eyes moved to look at Boromir. "But both of you would be reborn, for I will not see you separated from your soulmate now the two of you are united."
Kíli's questioning eyes returned to Boromir, asking his thoughts silently. To go back? To live another life...? Boromir searched Kíli's face, searched his very soul through the bond they shared. For a moment he thought about refusing but... With the faintest nod to Kíli he turned to Mahal. "If Kíli will do as you ask, then so will I, my Lord."
They would face life once more, bring their people home, and they would do it side-by-side, with one another's support all the way.
Boromir had only found true life after his death. He would not let it go ever again, no matter what trial he and Kíli faced.
A certain little gemstone probably found her way to a certain redheaded Elf. Maybe in their new lives, Kíli and Boromir will meet them.