Hunt for the First Blade

The Hunt for the First Blade was a hunt undertaken by hunters Sam and Dean Winchester along with the King of Hell Crowley to locate the First Blade in order to kill the Knight of Hell Abaddon.

Background
Millennia ago, when Cain discovered that his brother Abel was talking to Lucifer, he made a deal with Lucifer where his soul would go to Hell in exchange for Abel's going to Heaven. Lucifer demanded that Cain kill his brother and send him to Heaven as well and Cain did so, crafting the First Blade for the job. Lucifer cursed Cain with the Mark of Cain, a curse that kept the Darkness at bay and caused a bloodlust in the wielder. Eventually, the atrocities the Mark caused him to commit was too much for Cain and he killed himself with the First Blade. However, the Mark of Cain refused to let Cain die and resurrected him as a very powerful demon.

As a demon, Cain created the Knights of Hell under the orders of Lucifer, creating an order made up of purely evil demons who committed atrocities across the Earth for centuries. Cain eventually fell in love with Colette Mullen and retired to marry Colette who asked him to give up his evil ways in exchange for her love. Cain complied, but the Knights of Hell kidnapped Colette to try to force Cain to return to them. In response, Cain took up the First Blade, the only weapon that could kill a Knight of Hell and slaughtered the Knights in revenge and to rescue Colette. Eventually, only Abaddon was left and she possessed Colette to get at Cain. When Cain refused to return to his evil ways and join her, Abaddon started snapping Colette's bones. Cain attempted to kill Abaddon with the First Blade, but she fled Colette's body, leaving Cain to kill Colette instead. At Colette's request, Cain didn't chase down Abaddon for revenge, letting her live and throwing the First Blade to the bottom of the Mariana Trench, the deepest part of the ocean he could find as the First Blade couldn't be destroyed.

Abaddon eventually resurfaced in 1958, creating a "demon factory" where she stole souls to transform them into demons and slaughtering the Men of Letters. After being defeated while searching for the Key of the Order of Letters in 2013, having followed Henry Winchester there through time, Abaddon was put back together by Sam and Dean Winchester in hopes of curing her to complete the Trials of God. Abaddon escaped, but not before she learned that Crowley was now the King of Hell to her disgust. Abaddon reemerged after the Winchesters had captured Crowley, intending to kill him and take over Hell for herself. However, Sam doused Abaddon in Holy Fire, forcing her to flee her vessel Josie Sands and foiling her attack on Crowley.

After her attack on Crowley was foiled, Abaddon had a loyal demon restore Josie's body for her to use as a vessel. Abaddon then began gathering a following to take over Hell for herself and then eventually the world, attacking the Winchesters in Eugene, Oregon before fleeing when Gadreel revealed himself nearby. With Crowley captive in the Men of Letters bunker, Abaddon took advantage of his absence to start reshaping Hell to her desires, calling in soul deals early in order to boost the soul count in Hell. After helping to free Sam from Gadreel, Crowley was set free and informed Abaddon that he intended to wage a campaign against her for rule of Hell, fighting for the "hearts" of the minor demons to see who would rule Hell.

Battle
Shortly after separating from Sam after saving him from possession by Gadreell, Dean is approached in a bar by Crowley. Crowley tells Dean he needs Dean's help to kill Abaddon by locating the only weapon that can kill a Knight of Hell, the First Blade. Crowley explains that he's been hunting for the First Blade for decades and the closest he got to it was when one of his demons, Smitty, learned of a protégé demon of Abaddon's who claimed to have knowledge of the First Blade. However, John Winchester had captured the demon before Smitty could get to him and Crowley suggests that there might be some information on the First Blade in John Winchester's Journal. Dean reluctantly checks the journal which confirms that John did capture the demon Smitty had been after, but is unable to find much more. At Crowley's insistence, Dean admits that a series of numbers in the margin refer to John's Lock-Up and suggests that John may have left more information on the case there. Though reluctant to trust Crowley, Dean agrees to check the lock-up in hopes of finding a clue on the location of the First Blade. Unknown to Dean, one of Abaddon's demons spots them and begins following them.

At the lock-up, Dean searches through John's case files and finds one on his capture of Abaddon's protégé. Dean learns that John worked with another hunter named Tara and exorcised the demon after an interrogation, during which the demon mentioned the First Blade to John and Tara. However, the file is empty of anything else so Dean decides to have them locate Tara in hopes that she's still alive and can tell them something more about the location of the First Blade.

Dean and Crowley locate a Tara at a pawn shop she runs and Dean introduces himself as John Winchester's son. However, Tara feels a pain in her knee that lets her know when a demon is near and aims a shotgun at Dean and Crowley who is left stuck in a devil's trap hidden under a rug in the pawn shop. Tara initially believes that Dean is possessed since he is working with Crowley, but he is able to prove he isn't when she splashes him in the face with holy water. Dean explains that Crowley is helping him on a job and that Tara and John had captured a demon who knew something about the First Blade and they need to find the weapon. Dean continues on to explain that they need the First Blade as they're hunting a Knight of Hell and that they're not all dead as was believed since Abaddon has returned. Convinced, Tara shows them her notes on the case, explaining that the demon they captured told them that the archangels used the First Blade to kill the Knights of Hell. Neither of the two had ever heard of anything like the Knights of Hell or the First Blade and John thought the demon was lying to save himself. After they exorcised the demon and went their separate ways, Tara started looking for the First Blade, believing that such a weapon could give a hunter an edge. However, after searching all over the world, all she could find was a location spell for the First Blade she couldn't finish. When Crowley learns that Tara couldn't finish the spell because she couldn't find the last ingredient which is essence of Kraken, he reveals that he can help as he has "a warehouse full of Kraken essence in Belize." At Dean's insistence, Tara reluctantly breaks the devil's trap so Crowley can get the Kraken essence. While Crowley's gone, Tara warns Dean about working with him, but Dean says that Abaddon is way worse and he can deal with Crowley after killing her. Crowley returns with the essence of Kraken and Dean performs the location spell which points to a spot in Missouri. Though they offer Tara the chance to join them, she refuses to work with Crowley and remains behind as Dean and Crowley head to the location the spell indicated.