So like this you mean:
Old Xerath lore
In the ancient civilization of Shurima, the mage called Xerath practiced magic with undying passion. He believed that with enough magical power, he could gaze into the heart of Runeterra to know the secrets of history and the universe beyond. Such magic was beyond the limitations of a mortal body, but Xerath obsessively pursued a path to infinite power nonetheless. With every breakthrough he grew more and more powerful, yet not without consequence. Xerath's increasing arcane abilities wrought havoc on his physical form. Desperate, he undertook a dangerous ritual to transcend his dying body. The outcome would be immortality or self-destruction. Violent magic unleashed during the ritual caused devastation throughout Shurima, but when the dust settled, Xerath emerged as an ascended being of pure arcane energy.
Free of flesh and bone, Xerath held nearly infinite power at his command. However, in the wake of his chaotic ritual, the mages of Shurima feared his careless disregard for life would bring ruin to the kingdom. After a terrible struggle they subdued Xerath, but they could not destroy his ascended form. Instead they trapped him within an enchanted sarcophagus and sealed him in an underground tomb. Eons passed, civilizations rose and fell, and Xerath's imprisonment was lost to memory. For centuries, Xerath's vast power tore away at the sarcophagus and weakened its spell. Finally, he willed forth a burst of magic that shattered his prison, but its core remained, containing Xerath and his power within its broken pieces. Seeking to rid himself of this burden, he was drawn to the magic of Valoran's nexuses and found he could absorb their power. Yet the nexuses had gatekeepers: petty mages known as summoners. Xerath knew his key to true freedom from his prison lay in gaining their trust, and he offered his power to the League of Legends.
"I have no need for vengeance. Time has brought ruin to the mages of Shurima and I alone remain."
― Xerath, the Magus Ascendant
New Xerath lore
Powerful beyond reckoning, the ascended being known as Xerath was once a mortal of flesh and blood. He is now something vastly different - a being of writhing arcane energy. Having emerged from millennia-spanning imprisonment, he is now ready to unleash his power upon Runeterra, and utterly destroy any who oppose him.
The True, Complete lore: UNBOUND
This was the moment.
The singular moment that had cost him so much, that had taken a lifetime of planning. A corrupt empire and its strutting princeling would be struck down under the blankly idiotic sun symbol they both so trusted. The key to immortality, jealously guarded and miserly offered, would be his alone, stolen in front of the entire world. A singular moment of perfect vengeance that would finally free the slave known as Xerath.
Though his Azir master's helm revealed no human expression, and knowing that the lovingly etched metal could not respond in kind, Xerath smiled up at the Azir soulless hawk's face just the same, his joy genuine. A life spent in servitude, first for a mad emperor and now a vain one, endless manipulations for and against the throne, a near-damning quest for barely remembered knowledge that almost consumed him—all of it led to this grotesque masquerade of Ascension.
The very word when spoken aloud was an assault: We will Ascend, while you are chained to the broken stone as the sands of time swallow you all. No. Not anymore, and never again. The chosen golden lords will not be taken into the sun’s embrace and made gods. A slave will do this; a simple slave, a boy who once had the misfortune to save a noble child from the sands.
And for this sin, Xerath had been punished with a horrible, maddening promise: Freedom. Unobtainable. Forbidden. Should the thought even dart through a slave’s mind, it would be punished by death, as the Ascended could gaze past flesh and bone, deep into one’s very soul, to see its dim traitorous glow. And yet, there it was, spoken by the young princeling he dragged from the embrace of the mercurial mother-desert. Azir, the Golden Sun, vowed that he would free his savior and new friend.
A promise unkept to this day. The words of a grateful child, innocently oblivious to the impact they would have. How could Azir upend thousands of years of rule? How could he fight tradition, his father, his destiny?
In the end, the young emperor would lose it all by not honoring his word.
And so, Xerath was elevated and educated, eventually becoming Azir's trusted right hand—but never a free man. The soured promise ate into what he was, and what he could have been. Denied a small, simple thing, the right to live his life, Xerath decided to take everything, all of the things denied to him, all of the things he deserved: the empire, Ascension, and the absolute purest form of freedom possible.
With each step taken toward the offensively grandiose Dais of Ascension, positioned respectfully behind his emperor and flanked by the inept sentinels who supposedly protected Shurima, Xerath felt an unknown lightness he was genuinely shocked by. Was this joy? Does vengeance bring joy? The impact was almost physical.
At that very moment, the overwrought suit of golden armor that was his tormentor abruptly halted. And turned. And walked toward Xerath.
Could he know? How could he possibly know? This spoiled, self-obsessed boy? This righteous, falsely benevolent emperor whose hands were just as bloody as Xerath's own? Even if he did, there was no staying the killing blow that was already in motion.
Xerath had planned for every contingency. He had bribed, killed, out-maneuvered, and plotted for decades—he even tricked the monstrous brothers Nasus and Renekton into staying away from the event—but he had not planned for this...
The Emperor of Shurima, the Golden Sun, Beloved of Mother Desert, soon to be Ascended, took off his helmet, revealed his proud brow and smiling eyes, and turned to his oldest and most trusted friend. He spoke about the love of brothers, the love of friends, of hard fights won and others lost, of family, of future, and finally... of freedom.
At these words, the guards flanked Xerath, moving in, weapons drawn.
So the princeling did know. Had Xerath's plans had been undone?
But the fools in armor were saluting. There was no menace to them, they were honoring him. They were congratulating him.
On his freedom.
His hated master had just freed him—he had freed them all. No Shuriman would ever wear chains again. Azir's last act as a human was to unfetter his people.
The foundation-shuddering roar of the assembled masses drowned out any response Xerath could have had. Azir donned his helmet and strode out onto the Dais, his attendants preparing him for the godhood that would never come.
Xerath stood in the shadow of the monolithic Sun Disk, knowing that an empire-destroying doom was but seconds away.
Too late, friend. Too late, brother. Far too late for us all.
