I already have an idea for an updated Xin bio.
Xin Zhao was born in the Ionian village of Wuju and grew up with his younger brother, Yi Zhao (who we know as Master Yi).
While Yi was a natural talent at learning the ways of the Wuju Style, Xin was rash and impatient and never managed to master it to the same level as his brother.
Repeatedly scolded by his peers, Xin was eventually relegated to helping his parents in their workshop, forging the very same weapons he never managed to master.
Xin was envious and resented his brother for succeeding where he failed, and channeled all of his anger and hatred into forging a weapon to slay him in secret.
After a hundred nights, he succeeded, having forged a pristine sword with 2 rings.
He named the ring sword "Highlander", citing that there can be only one heir to the Zhao family name.
Xin found himself keeping a silent vigil over his brother as he slept countless times, tempted to, but never being able to bring himself to slay him.
He often pondered if he was supposed to be here at all. He would look out and see faraway towns no one else ever mentioned.
Though the elders forbade leaving the village, Xin ran away from home, seeking his destiny elsewhere.
Before leaving, Xin revealed the truth and gave Yi the sword he intended to slay him with. In a twist of irony, Yi would be the one to stay, and Xin the one who should go.
Travelling east, he found himself working at the esteemed Kashuri Armories in Zhyun. Though he attempted to, he would never be able to replicate the Highlander. However, for a time, Xin found peace with himself.
That is, until the invasion.
When Noxus brought war to Ionia, Xin was one of the first to answer the call. He would travel from town to town, arming the local defenders with the highest quality weapons and armor to stand against the Noxians, though in his heart, he longed to be the one sent to fight.
That opportunity came during the Noxian occupation of the Placidium.
Though he was about to enter a battle he knew he had no chance of winning, Xin grabbed a spear, and audaciously charged at the invaders.
Hopelessly outnumbered, the Noxians found his will to fight no matter the odds amusing, and captured him in order to be forced to partake in the Fleshing.
The Fleshing was a gladiatorial event with a cruel twist: as a fighter won matches, his number of opponents (generally other prisoners of war) fought simultaneously would increase. This meant eventual death for every contender, but with unparalleled glory.
During his time in imprisonment, Xin would meet a wide range of different people from all over the world, all captured to fight endless battles for the entertainment of Noxus' wealthy leaders, and would often be forced to slay them shortly afterwards.
For his many victories, he would come to be known as "Viscero", Ur-Noxian for "Unstoppable".
As his success grew, he would eventually be pitted against a Minotaur from the Great Barrier, Alistar.
Though it is not known why, for the first time in Fleshing history, the two fighters teamed up in order to defeat the rest of the opponents. When they were the last two standing, they refused to slay the other.
Under normal conditions, both fighters are to be summarily executed by dawn. However, Xin's popularity kept him alive for now, the Minotaur instead being the one to take the fall.
Most notably of all, however, Xin would eventually meet the prince of Demacia, Jarvan IV, in one of the many slave encampments spread across the Noxian countryside.
They quickly found a common contempt for Noxus, and the young prince shared many stories of his original home, though he no longer found himself worthy of it. Xin, though also lacking purpose, would be the one to keep up his spirit during these trying times, sharing stories of his own. The prince promised that if they ever make it out alive, he would always be welcome in Demacia.
The next day, Xin was slated to face 300 soldiers, nearly six times the previous record. This was clearly meant to be his final match, were it not for an attack on the encampment in the dead of night by Garen and The Dauntless Vanguard.
Though the Demacian warriors could not reach them, they used the distraction to fight their captors and escape. As the prince ran, Xin stayed behind to fight off anyone that would run after him.
When Garen and his men discovered the Noxian camp, they only find a battered and bruised Xin standing next to Jarvan’s armor, discarded next to a bloodsoaked executioner’s post.
Xin told them that he had stayed behind to protect the prince, who fled into the wilderness. This act of loyalty, from a man who vowed no allegiance to the prince, earned Xin Zhao a permanent home in Demacia.
Now in the service of his new king, Jarvan III, Xin Zhao continues to fight for his adopted country and honor the legacy of the man who gave new purpose to his life.
Basically, I aimed at revealing more of his backstory (that I made up myself, that is), whilst keeping most of what we already have intact (replacing Jarvan II with Jarvan IV).
and 
(who may I mention got his color story without a bio when Ezreal got updated).
