Arya Stark is the second daughter of Lord Eddard "Ned" Stark and Lady Catelyn Stark of Winterfell, growing up in the castle of Winterfell along with her brothers and sisters, Robb, Sansa, Bran, and Rickon, as well as Jon Snow, who was first thought to be Ned's bastard son. From childhood, Arya was a fiercely independent girl, with no interest in "ladylike" pursuits, instead of having an interest in weapons and warfare, and a desire to learn to sword fight, unlike her sister Sansa, who she has a strained relationship with.
After Ned Stark is named Hand of the King by King Robert Baratheon and Sansa is betrothed to Robert's heir, Joffery. Because of this, the Starks travel to King's Landing. On the way, Arya meets has her first run-in with Joffrey which leads to Sansa's dire wolf Lady being killed as punishment.
Once in King's Landing, Arya receives sword fighting lessons from Syrio Forel who later defended her, who later defends her from Ser Meryn Trant after Joffrey ascends to the throne and kills the Stark household. Arya attempts to witness her father's trail, but was spotted by Night's Watch recruiter Yoren who had her pose as a boy and smuggled out of the city along with the Night's Watch recruits.
Thanks to these events Arya gained a strong sense of revenge and vowed to kill those who harmed her family and friends. During her travels, she temporarily acted as Tywin Lannister's cupbearer, befriends and becomes the lover off Gendry (the last of Robert's surviving bastards), and trained under a cult of assassins called the Faceless Men, killed those responsible for Catelyn and Robb's death before returning to the North and reuniting with her family.
Later she partook in the Battle of Winterfell and was ultimately responsible for killing the Night King and (by proxy) the other White Walkers. After Daenerys Targaryen's war for Westeros, Arya decided to explore the world and lead an expedition to the east of Westeros.
Battle vs. The Thief (The Invincible Soldier) (by SPARTAN 119)
Along a road, somewhere in the Vale of Arryn, Westeros
Arya Stark walked along the lonely road leading the the port of Gulltown, where she would catch a ship, intending to travel to the Wall to meet her half-brother Jon Snow. At her side, Arya carried her sword, "Needle", as well as a dagger and a bag of coins taken from here now-dead captor turned traveling companion, Sandor "The Hound" Clegane.
From out of the woods, a figure appeared, a girl a little older than Arya, with strawberry blonde hair, wearing an odd outfit, a white shirt, a green cape, a pair of plate vambraces, but no other armor, and, most oddly to Arya's eyes, a pair of what a person from 21st century Earth would describe as "shorts" and stockings, but had never before seen in medieval Westeros.
"Fat sack of coin you've got there, Arya Stark", The Thief said in a foreign-sounding accent, though she had clearly been in Westeros long enough to understand the common tongue.
Arya's face displayed a look of surprise, how did this oddly-dressed smallfolk know her name? Arya said, "I don't know who you are talking about. I am not this Arya Stark person you are looking for.".
"Don't play dumb, the look of your face betrayed everything", The Thief said, "I'll be taking that sack of coin, and then I'll taking you to that knight lady, Brienne of Tarth. She seemed very interested in you, I suspect I could get a few Gold Dragons out of her in ransom."
Arya realized immediately the the thief must have been talking about that woman in armor with the Valyrian steel sword that killed the Hound. She must be working for the Lannisters.
Arya unsheathed Needle and held the rapier in front of her in an aggressive stance. She then thrust her sword at the Thief, who drew her sword and swung it downwards, parrying Arya's thrust.
Arya jumped backwards, out of the bind, only to be greeted by a wide horizontal swing from the left aimed at throat from the Thief's longsword. However, she managed to parry the the attack, swinging Needle to position. The longsword ground along the side of Needle, before being stopped by the ring-shaped sideguard. Holding her foe's sword in the bind, Arya drew the dagger she had taken from The Hound and thrust it forward.
The Thief raised her vambrace-clad wrist, parrying Arya's dagger strike, the dagger glancing off the steel armor. The thief then stepped backward and took downward swing at Arya, which she parried, along with a a second diagonal strike, rapidly moving Needle into position with a flick of her wrist.
The Thief then pulled her arm back, sword over her shoulder, as though about to thrust. Instead, however, she brought her arm around and made a powerful downward diagonal slash at Arya. Arya parried the strike, but the force of impact was such the grip was levered outwards forcing Arya's fingers open. Needle was knocked out of Arya's hand and send flying end-over end through the air, sticking point down in the ground several yards away.
Not one to give up, Arya picked up a stone from the ground and hurled it at the thief. She easily dodged and laughed. "Feel like giving up?", The Thief asked.
In the moments she took to dodge the rock, and then taunt Arya, the Thief had left herself open. Arya lunged at her with the Hound's dagger as she said "Valar morghulis"- "All men must die" in High Valyrian.
The Thief only just managed to raise her armored wrist in time to block the strike with the dagger, but Arya still hit her with the full force of the lunge, knocking the Thief on her back and causing her to drop her sword.
Arya thrust the Hound's dagger downward at Thief's heart, but the Thief raised her left wrist, and placed it in front of the blade. The point of the dagger only barely pierced the armor, little more than a pinprick. The held Arya's hand back as she drew her cinquedea with her left hand and slashed at Arya's neck.
Blood flowed out of the wound as Arya breathed her last, staining the Thief's white clothing. The thief pushed the body of her vanquished foe off of her.
"So much for the ransom", The Thief said as she stole the bag of coins Arya had. Then, the thief thought of something. She had not damaged Arya's clothes in the fight, and that Brienne had seen her only briefly, and with her cloak over her head. It wouldn't be that hard to don Arya's clothes, wear a cloak over her head to hide her appearance, and disguise herself as her victim. The she could cut that woman-knight's throat in her sleep and take that Valyrian steel blade. Then, it was only a decision, sell the sword for a king's ransom in gold, or keep the supernaturally sharp and durable sword for herself.
WINNER: The Thief
I've killed off one of the most popular character in Game of Thrones, bring on the anon-rage! In any case, the Thief won this battle because of her superior weaponry, as well as her greater amount of combat experience, having spent years fighting, stealing, and killing. The Thief also had plate armor vambraces, which only covered a small amount of her body, but allowed her to use her wrist to block attacks.
Arya Stark walked through the streets of Zchted, no one suspecting her true identity as an assassin of the Faceless Men. Personally, Arya was surprised that, after her failure to kill her intended target the first time, Jaqen H'ghar (or whoever he really was) had allowed her a second chance after recovering from the temporary blindness. In fact, she wondered if he had chosen this target intentionally:
The target in question was a high-ranking noblewoman and military leader in distant land called Zchted, a "Princess of War" or "Vanadis" as she was known. The target's name was Valentina Glinka Estes, a woman, who, behind her facade of a sickly young girl thrust into a position of power, was a power hungry and manipulative woman bent on seizing the throne, who didn't care how many people she had to kill to acheive her goal.
This woman had brought about the downfall of a noble house who suspected her, and, most recently, had turned two rival heirs to the throne against each other with an attempted poisoning. She was even rumored to be involved with the mysterious death of the Prince of Zchted. But it was not the throne who sent the Faceless Men after her, but rather, it was the family of the "food taster" of Duke Ilda Kurtis, a man who died of a poisoning, instead of Ilda himself. The Faceless Men would work for anyone, and ensure their price was one they could pay... however high it might be to them.
But what exactly the taster's family had paid was not her concern. Rather, while she had never met Valentina, she still felt a hatred for her... From the description, she reminded her of her hated enemy, Cersei Lannister.
Arya walked out for the town gates, towards a cliff with a view of the castle of Osterode. The castle was much smaller than the Red Keep, indeed, not much larger than the House of Black and White in Braavos. Still, it had a second gate, barring entry from the town to all not authorized to enter by the Vanadis. The gate and walls were ringed with towers manned by crossbowmen and armed with ballistae. Arya did not think attempting to climb them was a good idea.
Then she saw it: it was an entrance of a wide tunnel going into the castle from the sea. It was presumably an exit for the garderobes- medieval toilets. It wasn't the cleanest approach, but it was the critical weakness for this fortress. Tonight, Arya would brave the waters to strike her target.
Later that night
Arya Stark climbed out of the foul water in the drain, and crept onto a narrow stone walkway running along the primitive sewer running out of Osterode Castle. The up ahead, a lone guard armed with a spear had his back turned.
Arya lunged forward and thrust her rapier, Needle- the one piece of her past she had hidden from the Faceless Men- between the gaps in the guard's armor, straight into his heart from behind. The man was dead without making a sound. Arya pulled a mask out of a small sack at her belt, and donned it, transforming into a young man.
Arya then then spent the next several minutes changing into the guard's armor and clothing, as well as taking his spear and then tossed the dead man's body into the sewer, which flowed out into the sea. Arya donned walked up into the main castle, disguised as a guard.
Because of the lingering smell from literally entering through a sewer, she had to be careful not to get to close to anyone. Thankfully at this deserted hour, there were only a few guards walking about, which were easily avoided.
After about 20 minutes of creeping about in the castle, she had found her way to the bedroom where her target slept. Arya raised the spear she had stolen from the guard she was now disguised as and thrust it toward the sleeping form of Valentina Glinka Estes.
Then, the unexpected happened: Valetina rolled out of bed, and grabbed Ezendeis, which stood propped against the wall.
"Ara ara", Valentina let out her trademark laugh, before she said in Zchtedi, "It appears I have company"
Arya did not understand a word of the language, and instead, simply thrust the spear forward a second time, only for Valentina to dodge the swing, and slice the handle in two with a swing of Ezendeis.
Furiously, Arya, drew Needle and, aiming by the light of the candles on the table and full moon in the window, thrust it forward with a shout of "Valar Morgulis!"- High Valyrian for "All men must die"
Valentina, however, simply spun Ezendeis in a circle, and disappeared in a circle of pure blackness.
"What the!?", Arya yelled, but was cut off by the sound of a footstep behind her. Arya turned on the spot, in time to see Valentina behind her, raising her scythe. Arya jumped backwards, only barely being grazed across the face by the strike, increasing her resemblance to a certain halfman of House Lannister
The strike had also knocked off the mask from Arya's face, revealing her true form, and causing the armor to fall off her true, young female body, leaving her only in her underclothing- similar in appearance to a white nightdress- given the fashion in medieval Westeros, it was still more modest than Valentina's revealing dress, which Arya thought made her look like a whore.
Furious at this humiliation, thrust her sword forward, but was blocked by Valentina, who blocked the attack, and retaliated with inhuman speed. Arya rolled out of the way and immediately got back up. Even with all the training of Syrio Forel, she could only barely dodge Valentina's attacks.
"I see you speak Asvarri", Valentina said, in what, to Arya's surprise was perfect Westerossi, "Who are you? If you spare my life and work for me, I could make it worth your while".
"I am no one!", Arya replied, and responded to Valentina's proposition by thrusting foward with Needle, straight at Valentina's heart. Valentina raised Ezendeis, and Needle glanced off the handle, being redirected. Valentina let out a scream of pain as blade pierced her.
It was not a fatal wound, but the blade had pierced through Valentina's right breast at a diagonal angle, but had missed piercing her vital organs. Arya pulled out Needle and went in for another attack, but Valentina recovered and swung her scythe furiously, forcing Arya to jump to the side.
"You will pay most dearly for that!", Valentina said as she furiously attacked Arya.
"Hmmph, what kind of warrior cares about a few scars!", Arya taunted her adversary.
"Do you know who your are dealing with!?", Valentina said, "I am the future queen for Zchted!" As she spoke, Valentina teleported behind Arya, in the middle of sentence, immediately revealing her location.
Arya did not know how she did that, but she know one thing: Valentina was not a very experienced fighter, if she advertised her locations so easily.
Arya thrust her Needle towards Valentina, only for Valantina to spin her scythe as though teleporting, but instead, the blade simply struck Needle and knocked it out of Arya's hand.
Valentina then pressed her advantage, thrusting the secondary blade of Ezendeis downward, into Arya's foot, causing her to scream in pain and fall backwards. Valentina then walked directly on top of Arya and said:
"To tell you the truth, I'm surprised you lasted so long against against a Vanadis like me, but in the end, nothing will stop me from ascending to the throne", Valentina said, before breaking into Zchtedi (which sounds a lot like Russian) "Da Svadanya, no one!".
Valentina then trust the secondary blade of Ezendeis down into Arya's heart, spraying blood everywhere as the Vanadis of the Shadow let out a maniacal laugh.
The experts believed this was very close match, as seen in the simulation where Valentina was severely wounded in the fight. In the end, however, Valentina's superhuman abilities and natural talent for deception allowed her to overcome the superior training and the abilities of the Faceless Men's masks that Arya possessed.