this is a combo of book and movie canon because I'm picturing the movie scenes but Estel is ten and Glorfindel is there so its a fun mash-up.
Also nearly everything about Elf weapons, Gondolin, and other Middle Earth Canon is me making stuff up. I am full of b*llsh*t so if you see something you don't recognize as fact, don't take it as canon.
Glorfindel managed to keep his composure when Gandalf and Thorin showed off their new-found swords at the high table of the feast of their arrival. It was difficult but he persevered, fist clenched on his thigh under the table and breathing to the tempo of exercises he had taught to anxious recruits over centuries.
Glamdring, Goblin-cleaver, was the mighty sword that had made powerful arcs from his King's hand; Turgon had chosen a straight hand-and-a-half sword design influenced by Tuor. It had been unique at the time, in culturally-inclosed Gondolin, and then become all the rage. Glorfindel himself had begun training with such a sword as a hobby during those last years. That blade had been little used and had been left in the burning wreckage of the physical House of the Golden Flower.
He had known Glamdring well enough, but Orcrist had been heartbreakingly familiar to him.
It was perhaps the sword he had used second-most to his own melted, shattered blade.
He and Ecthelion had trained daily together, tossing blades to trade and practice different styles or ready themselves for an emergency where only the other's weapon was available.
Orcrist was in the same curved style as his own sword preference, but was meant for primarily one-handed use. In Gondolin, Glorfindel had a heavier, larger two-handed weapon. Had it been his blade that survived, he doubted that the dwarf-king would be comfortable wielding it.
The sword was being passed around the table, and his hand was reaching to take it from Elrond's hand before he could consider whether or not he actually was prepared to touch it again.
It felt the same as always, metal mildly cooler than he was used to, not yet warm from Ecthelion's grasp, but still keenly sharpened, still perfectly weighted, still gleaming with engravings and embellishments. It had been meticulously treated by Ecthelion- his prized possession (aside from that fountain). And a painful nostalgia struck Glorfindel, and he ached return to the time of teasing insults tossed between them. Ecthelion would tug his hair calling it Glorfindel's vice of vanity, and he would reply with a threat to drown Ecthelion in his own fountain.
But Ecthelion and Gondolin and the fountain were gone and there was a Dwarf King looking expectantly at him.
"It was a beloved blade. Your cause would please its first owner. Honor it well." It was as much as he could manage without revealing too much or losing dignity. Perhaps he would compose a letter detailing its past to Thorin once Erebor was regained. He had faith in the company, and his own hope that they would succeed. His voice was not among those admonishing them during that meal.
It was the next day, in a chance encounter in a garden that the little Hobbit's weapon that shattered his resolve. He had come across the hobbit imitating training movements with the blade on a secluded loop of path.
Bilbo let on that he had been content to let it be dismissed as a "letter-opener" or dagger, but it was not.
Glorfindel had not said much to the hobbit. Merely looking it over and confirming that there was no name known for this particular weapon. He was certain it had had one, but it was not engraved.
Then Glorfindel returned the blade to its new owner, hastily, before his hands could begin to shake. And he left him to the gardens.
Glorfindel himself ended up in a dark hallway, before the massive tapestry depicting the Fall of Gondolin in aged thread. He did not spare his own vibrant likeness's tragic ensnarement a glance, but instead fixed a glazed stare upon the burning city and the exodus of vague elf shapes spilling from it.
He had known the hobbit's blade, or had known dozens just like it.
It was a child's blade. The kind given to youths who wanted to join the guard but had only reached the second levels of training - after wooden blades. Before they were allowed a full sword they were given the knives. Longer than a dagger, they were more ceremonial than really used. They were prized by the elflings who received them and often given fanciful names reflecting the hoped-for goals of the owner. Bilbo's weapon had likely been called "Destroyer of Dragons" or "Orc's Nightmare" or something of that ilk.
To be found like that, with the blades of warriors like Ecthelion, meant it had seen more battle than anyone had ever intended. Here was proof again of what he had always known - that the evacuation had not been entirely successful.
In place of the woven wall-hanging, he saw snippets of that last day , scenes that he had spent millennia forgetting, of small bodies lying still and broken - Rog's daughters, Ecthelion's little cousins, and the to-be-archer from his own house who had had Glorfindel preside over her majority celebrations the week before the attack. And their faces changed from what he remembered to others, Eärendil, when Glorfindel had known him had one of the knives (named Valar's Might), and his features turned to Elladan and Elrohir, Arwen, Lindir, Rúmil, Legolas, every elfling he had been present in any way for the raising of could have been one of the children lost in Gondolin.
In Valinor, and since his rebirth, many had praised him for the refugees his sacrifice has saved. But it would never feel like enough compared to the countless others whose lives ought to have been immortal but instead were cut brutally short.
Gondolin was a massacre that was known by every elf, but to most it had become faded in comparison to later kinslayings and battles, and then by millennia of passing time.
For Glorfindel, the memories were kept fresh by nightly recollections of his own death. Gondolin was kept as an ever-present memory both treasured and detested in his heart.
It was a week before Elrond could spare him and the valley was deemed completely free of orcs. Of course, Glorfindel had been ready to ride out and investigate that evening, but a talking-to by the combined personalities of Elrond and Erestor had forced him to scrounge up enough patience to wait the days.
And thus he had spent a jittery week looking out the window from his office, getting busy work shoved into his hands by Erestor, and training with a variety of weapons in any modern style he could find a partner for.
The dwarves had proven helpful in that. Once he had gotten him away from his uncle, the young archer had quickly warmed up to trading tips and techniques on the practice range, and a few of the older warriors had been willing to test their mettle against an ancient elf-lord even they knew legends of.
And now, finally, he was clambering into a reeking troll hoard with a lantern and four companions.
Erestor had come for moral support and to help identify where artifacts had come from, Elladan and Elrohir had come because Erestor decided this counted as a "history lesson". Little Estel had followed both because he did not want to miss out on the excitement, and because all four of his main minders were going and Elrond and Gilraen were busy with the aftermath of the Dwarves' visit.
The twins were keeping the ten-year-old away from anything really sharp and holding lanterns which left Glorfindel's hands free to search the cobweb-coated items.
More swords were found, along with a few rotted old quivers, broken helms and chest-plates from past centuries of elves and men, dwarvish jewelry and knick-knacks, fragments of a shire pipe and set of wood furniture, and then a pile of gleaming Gondolindrim armor.
But not all of it was in good condition.
A rounded shape caught Erestor's eye and he pointed to it, beckoning a cautious Glorfindel over. With reverent, battle-calloused hands he lifted the once smooth silver of a pointed helmet.
It was dented and scratched, with the filth of the ages ground deep into marred marks, and worst of all, the spike on top was a misshapen mass, melted in the heat of a Balrog's torso. On a proud head had this helm once rested.
It smelt still of burning, and Glorfindel turned it slowly in his hands, loathe to look at the inside.
He dropped it with a dull thunk on the dirt floor of the cave. A few strands of long black hair were yet stuck to the inside of the helm. Glorfindel smelled charred flesh and heard the roaring of unintelligible screams fill his ears.
He turned aside and fell to his knees, retching, the stench of the troll hoard doing nothing to alleviate the phantom stink. He felt Erestor's hands pulling him toward the exit and fresh air, and vaguely noted indistinct questions from Elrond's sons.
The warm breeze outside extinguished the flames in his mind, and his thoughts cleared. He did not regret coming to search the stolen relics, and did not regret finding Ecthelion's helmet, as painful as the images it evoked were. But he wished with every fiber of his being that none of it existed. That Gondolin had not fallen to treachery and ruin. But that was an old wish, an old want that centuries in Mandos's halls and millennia living back in the world had taught him to tamp down to a back part of his mind.
He could not change the past, he could only do his part to ensure that Imladris, and hopefully no other future city, ever fell in the gruesome way that Gondolin had.
Glorfindel had not re-entered the troll hoard, instead packing what was already extracted into their saddle-bags and then waiting.
Later, in telling Elrond of their find, the twins revealed that they had brought the helmet and after consulting Glorfindel and giving him time for consideration they cleaned it. It received a place of honor with the other identified armor in a hall in Imladris.