Okay so mercurygray prompted me with this on tumblr and then cello asked for it posted here and how can I deny either of them anything...?
Thorin was grieving his grandfather and king, as well as his nadadith, when he led the charge on the orcs of Moria. He could not think past the battle, past his grief, and so when it was finally over he felt at a loss.
Frerin was down in the woods by Mirrormere, and nearby was Fundin son of Farin. By the time Thorin made his way back to the woods, back to his brother, Dwalin and Balin were mourning their father.
Frerin had been in the first charge. His armor had been the best they could find for him, but nothing like he'd have had if they had still had Erebor. Frerin would have had no need to join this battle if they'd been in Erebor.
Frerin had been too young to be here.
Thorin wished to grieve as many others were doing. He wished to clutch his brother's body close and neaten the braids that had become disheveled. But Thorin felt the weight of those who survived watching him, looking to him. His was a prince of Erebor, and he knew that he had to put aside his own grief until later.
Later turned out to be much, much farther along than he'd anticipated.
They burned the bodies, Frerin among them. There was no way to bury them all in stone, no way to bring them back to waiting families. Thorin kept a few of Frerin's beads carefully hidden away, to give to his sister and keep for himself. He doubted his nadadith would have minded.
Thorin was left to rule on his own; there was no time for grieving. They settled in Ered Luin, not far from the ruins of Belegost. Dis lost her husband, was left to raise two young dwarflings on her own. His nephews got into all kinds of mischief, reminding him so painfully of Frerin and him in Erebor. Thorin let the work of making sure his people were prosperous and safe consume him.
It was Dwalin who eventually dragged him to his sister's home, and it was then that Thorin finally mourned for his brother properly.
He hadn't thought he needed to. He would have assured any who dared ask (and very few would) that he had mourned his brother and was fine.
He saw Frerin everywhere in Dis' home. He saw his nadadith in Fili's huge, mischievous smile, and Kili's constant cheer and curiosity. His brother was in the whispered huddles when his sister-sons plotted a prank to perform on Balin to escape lessons, and in their preference for turning weapons lessons into a wrestling match between them, and in the sweet rolls Dis made for breakfast sometimes.
Frerin was everywhere, like the faintest of echoes, but Thorin did not break until the night his nephews came to him after their baths and asked him to do their braids.
In their hands were familiar beads, Frerin's beads, and their eyes pleaded much the same as Frerin's had when they'd been young and safe in the mountains.
Dis shuffled her sons off to bed and sat with Thorin while he grieved.
Frerin had been too young, and too good, and too important to have been at the Battle of Azanulbizar. Thorin couldn't bring himself to talk of his brother, but he started to allow himself to think of him, to mourn him, to miss him with a ceaseless ache that sometimes throbbed more harshly when his nephews did something that sent echoes rattling through Thorin's mind.
He would make sure they did not die as Frerin did, that no battles would reach them so young, and that if they did ever have to enter battle they were armed and protected by only the best that could be forged by their people.
Of course, nothing that could be made in Ered Luin could compare to the craftsmanship of Erebor.