The Warriors of the Crucible
Harry creates a 'freerider company'
Harry Potter goes digging through the remains of the Room of Hidden Things while he's grieving for Dumbledore at the end of his Sixth Year. He goes browsing, finding a lot of interesting things, some of which he takes with him in his schoolbag. In his bag: wand, Invisibility Cloak (sneaks into the Room), Marauder's Map, old Muggle Studies textbook (several 18th-19th century inventions, gift for Hermione), Crusades-trophy Saracen recurve bow (always accurate), 12th century longsword (Unbreakable, eternally sharp), a jeweled goblet, and a talisman (corrects his terrible vision while he wears it).
As he's exploring, he finds a strange glowing amulet with an engraved dragon seal on it. But what attracts him to it are the Latin words. When he reads them aloud (With Fire and Blood, the Dragon Awakens), he is suddenly engulfed by a blinding void of light and in front of him is a large stone door that is locked shut. On the door is an enlarged version of the dragon seal as on the amulet and an empty slot for the amulet to rest on. When he places the amulet in its place, the door swings open and he's pulled through it, the doors closing behind him. (Fullmetal Alchemist)
(10 years prior GOT)
Shortly after, he awakens in a forest filled with strange white trees with red leaves. He can faintly feel a bloodthirsty malice emanating from the trees and is quick to flee the forest, but he soon discovers that he's on an island. Crafting himself a crude raft, he departs and heads towards a large castle he can see in the distance. When he arrives at the castle, he is disgusted by the state of ruin it is in but also awed by it's almost incomprehensible size. Entering the castle under his Cloak, Harry seeks out a library and finds one. He spends days hiding and sleeping in one of the abandoned towers while he researches the history and geography of the lands.
Once he feels he's got a good understanding of the world, he decides to approach the Lady of the castle for patronage. Lady Shella Whent became quite interested in the young man when he claimed to be a magician of respectable talent, proving it by putting on a dazzling display of unquestionable magic. When asked for his intentions and desires, he admits to merely wanting shelter, food, and a willingness to aid in the castle's restoration. Against the advice of her maester, Lady Whent agreed with his proposal and set him to work on repairing and improving her House's towers, which he did with mind-boggling speeds.
Over the next few months, Harry would share with Lady Whent a variety of ideas for how she could bring life back into the castle and end its longstanding curse. This was started by tearing down all unnecessary buildings (including the cursed Kingspyre), bringing in smallfolk and putting them to work in building an actual settlement within the castle walls. He supplied the castle blacksmiths with several new ways of forging steel (Damascus and Crucible). He showed carpenters and other smiths various 'new' inventions to improve their lives (printing press, clocks, cast-iron ovens). Very quickly, the smallfolk take a liking to him since he isn't a Lord, is very respectful to them, and is always seeking to improve their lives.
However, the maester of the castle became very antagonistic towards him, always trying to get the Lady to throw him, blaming him for random problems, and declaring his magic to be tricks of light and smoke. Harry instantly knew that he was a magic-hater and (considering the barbaric era they lived in) suspected the man would try to assassinate him. To this end, Harry never ate with the Lady's household, preferring to dine with the smallfolk or alone and cooking his own food. Eventually, Lady Whent gave the maester an ultimatum to either shut up or be executed, forcing the maester into silence.
But he wasn't the only one who hated Harry for his magic. The local Septon vehemently declared Harry an evil being sent by The Stranger and a blasphemous heretic who worshiped false gods and who refused to see the light of the Seven and disavow his twisted dark ways. Despite the Septon's best efforts, however, the smallfolk had already gotten to know Harry fairly well and knew he wasn't a bad person. Although a lot of the more hardcore followers had started calling for his death or expulsion from the castle.
Thankfully for Harry, the Greyjoy Rebellion begins and Harry takes the opportunity to get out of the castle, to let the hotheads cool down, to see more of the lands, to meet more and new people, and to possibly coat himself in glory. He attaches himself to the Riverrun host and joins the army that's reinforcing Seagard. While participating in repelling several Ironborn assaults, Harry becomes acquainted with numerous hedge knights, freeriders, and armsmen. With this group of acquaintances, Harry leads a daring surprise attack on an Ironborn scouting party. Disguising themselves as Ironborn, they sneak into the Ironborn camp and torch it, stealing their three ships and sailing to Seagard. Using charts found in the former Ironborn captain's room, the Riverlands army is able to predict the next string of raids and successfully repels all of them (including Rodrick Greyjoy's raid on Seagard), killing many Ironborn and capturing/burning their ships. With the coast now secure, the army sets sail for the Iron Islands, two months ahead of King Robert's scheduled invasion.
While the Lords were puzzling over the way they could take their first island with as minimal loss of life as possible, Harry (granted access to the debriefing for his role in leading that first raid and allowing this to all be possible) is asked for his opinion by Lord Jason Mallister. Harry offers up the risky plan of sending a small strike team ashore during the night to disable the ships at port, kill any guards, and aid in the silent docking of the Riverland fleet during the dawn hours. Despite the idea having merit, none of the Lords were willing to risk their own men (most of whom couldn't even swim!) on what was likely a nearly-impossible if not suicidal mission.
Once again acting without orders or permission, Harry gathers his now-growing group of loyal friends and smallfolk to discuss their own plans. Many of them decide that if it means the war will be ended quicker, they will brave this potential death-trap of a crucible. That night, they set out and sneak ashore. Aided by Harry's (secret) spells of concealment, the men are able to succeed in their mission. They then signal the fleet by setting numerous ships alight in the very early dawn hours. Drawn by the fire, the invasion force quickly approaches and lands while the Ironborn are scrambling to rouse themselves from their drunken stupors, induced by their recent victories which lowered their guards against counterattacks.
The invasion of Blacktyde went off without a hitch, barely a dozen Riverlands men were killed. Harry and his 'crucible knights' were hailed as heroes by the armsmen. Though the knights and some of the lesser lords were somewhat angered and embarrassed, feeling that he'd somehow slighted them by doing a mission they'd deemed impossible. Once they'd secured the castle and posted guards along the port, they prepared themselves for invasions and siege from the neighboring Iron Islands. They were indeed forced to repel five such invasions over a period of three-months until the Royal Fleet and Army finally managed to arrive and begin conquering the other islands. Due the Ironborns' focus being on Blacktyde, the Royal Fleet was able to easily catch the besieging Ironborn by surprise.
Following King Robert's rapid victory over the rebellion, Harry was brought before the King and various high lords of the land. Though the Lords were mostly displeased that some no-name peasant would dare act out as he had, Robert immediately took a liking to Harry for his daring tactics and the clear courage and loyalty he inspired in 'his men'. Robert offered to grant Harry a boon for his rather strategically important part in accelerating the end of the rebellion. Harry asked for permission to form an Order of warrior-scholars (placing value on both intelligence and strength) who's sole purpose was to defend the smallfolk from raiders, bandits, and depredations from the lesser nobility, answerable only to the king himself.
Upon learning that Harry was hailing from Harrenhal, King Robert agreed and allowed Harry's new Order to be stationed within Harrenhal itself. Harry's first recruits were the surviving friends and acquaintances he'd made, that the various lords, knights, and smallfolk. Modeling his new Order after what he remembers of the Knights Templar, Harry had the Order swear vows of piety, poverty, celibacy, and obedience to the king. The Order's sigil would the same red cross on white that the Knights Templar used, with their words being 'Face the Crucible!' They decided to officially name themselves the Warriors of the Crucible, though they'd already become widely known as the Knights Crucible.
Despite being officially known as a royal force protecting the smallfolk, many people (smallfolk, knights, and lords alike) at first saw them as just another band of sellswords. But despite this negative assumption, the Knights' heroics in the war had garnered a lot of respect. And when word got out that they were willing to accept anyone, from smallfolk to bastards to high lords, into their ranks, a surge of members (mostly freeriders and hedge knights) came to enlist, swelling their ranks from a mere 11 to over 1,000 within a few months.
In the next few years, with help and permission from Lady Whent, Harry put his Order to work. First, he went about his plans of tearing down the cursed Kingspyre and other such buildings. Massive fields and pastures were set up, a small fleet of trading and transport ships that sailed from Harrenhal down to the Blackwater Rush to King's Landing. Harry continued to introduce more and more new technologies and inventions that hadn't yet been created (though he refused to give them gunpowder). Along with a strict training regimen that all members had to undertake, the Knights were soon starting to gain a lot of attention from the many of the players (Lords Paramount, King's Landing, maesters, and Septons). Despite rumors of Harry possessing powerful magic, no one could actually pin it on him. Even so, the mystery of that started adding a layer of mysticism to the Knights. Combined with Harry's inventions and the new knowledge he was sharing with them, the Knights quickly started gaining reputations as true warrior-scholars.
Their first 'test of conviction' came about 2 years after the Greyjoy Rebellion. Word reached them of a group of bandits preying on the smallfolk of Deep Den. Harry and a group of 100 Knights set out of the area. After a bit of covert operations, they discovered it wasn't actually bandits who were the cause of the trouble, but drunken knights under the employ of House Lydden. Harry sets up a trap, planting his Knights in areas that the drunk knights preferred, with orders to capture or kill as necessary. Meanwhile, Harry approached House Lydden to get their take on the situation, finding that they honestly didn't care about the smallfolk's wellbeing as long as their knights remained loyal. When Harry promised to hunt down and execute every knight responsible, the Lyddens thought he was bluffing or trying to get a payoff to look elsewhere. Thus, when they learned that the Knights Crucible (after less than a week) had already accomplished their mission, capturing 15 and killing more than 30 more, House Lydden was astonished and infuriated. While the Knights brought their captives to King's Landing to face justice, House Lydden went straight to Tywin. By the time Tywin had sent a raven to Cersei and Pycelle, Lord Arryn had already had the king's justice be served. News spread quickly through the Seven Kingdoms about how the Knights Crucible had actually lived up to their promise to the king, protecting the smallfolk of a kingdom who wasn't even in their own, humiliating not only House Lydden but House Lannister, without accepting a single bribe, and managed to get away with it! It was this news that really caused the fame and infamy of the Knights to rise to unprecedented levels as their membership rapidly started rising to around 10,000.
In the following years, many more such incidents started reaching the Knights Crucible as more and more smallfolk and even lesser lords started approaching them for help. The Knights Crucible quickly spread out from Harrenhal, setting up strongholds or being given shelter in most of the Seven Kingdoms, becoming renowned as fierce fighters who refused to retreat from battle unless they were outnumbered 3 to 1, possessed a quickly growing massive financial reserve to fund their various construction projects and maintain themselves. They'd not only actively protect the roads and smallfolk, but they'd start supervising the construction, repair, maintenance, or even demolition of numerous buildings, castles, roads, or bridges all throughout the kingdoms. They'd establish hospitals and schools for the smallfolk, independent of the Septs and maesters (who quickly came to truly despise and envy them) while also being free of charge. But for as widespread as they became, Harrenhal (specifically the Tower of Dread) remained the beating heart of their Order as it rapidly expanded into a full city. Harrenhal's chief exports were the new swords and armor that only a select few blacksmiths produced from Harry's Damascus steel, due to its strong physical resemblance to Valyrian steel. The Knights Crucible decided to have crucible steel swords become their own iconic weapons, blades that had already proven themselves to be near-equals with the fabled Valyrian swords (which were superior only due to magic). The secrets of producing crucible steel were among some of the most closely guarded secrets of the entire Order for that very reason.
When the War of the Five Kings broke out, the Knights Crucible declared neutrality. Instead, they tried to focus their efforts on protecting and sheltering the smallfolk from the depredations of the various armies that were tearing apart the Riverlands. At least, they were until Tywin Lannister led his army to Harrenhal with the intention of seizing the castle, crushing the upstart Order that had humiliated him and several of his vassals for the past few years, and claiming the untold riches that many 'knew' they now possessed. However, during the night, the Knights slipped away across the Gods' Eye and disbursed across Westeros, taking with them their vast wealth and much of the secret knowledge with them. They would continue to secretly aid the smallfolk throughout the remainder of the war, following the tenets of their Order, while awaiting their leader's summons to return and resume their posts, duties, and studies.
Knights Crucible = stationed in the Tower of Dread
Lady Shella Whent = Tower of Dread, Tower of Ghosts, Widow's Tower, Wailing Tower, Kingspyre