For roughly a decade, one of the bloodiest conflicts sense the Rune Wars raged on the continent of Ionia. Disease, theft, hunger, murder, and destruction ran rampant.
During the Invasion of Ionia, more than just death occurred. Slaves were taken. Families were broken. Homes were burned. Farms were pillaged. These horrific events created bad blood towards Noxus. Generations onward would hate the Noxians. Buildings can be rebuilt, lives can restart, and wounds can heal. But bad blood can't be cleaned.
As Noxus took over multiple provinces of Ionia, the Invasion appeared to be getting worse. Until the Calaimeyan Siege finally uprooted the last Noxians which would end the Invasion, Ionia struggled. The war never seemed to get closer to ending. Resources, including hope, were in high demand and low supply. People form both sides were becoming desperate, the difference was that Ionians had much more access to magics.
In order to cope with the carnage and loss, an unfortunate number of Ionians turned to religious extremism, to blame and reason with the hellish battle that was destroying their world. These extremists formed cults. In addition, once the invasion did end, and Ionia looked to reassess its place in the world, dark arts became increasingly popular.
As a result, the Polong formed. A vengeful spirit hell bent on its goal, it thirsts for Noxian blood. Specifically of those whom had influence or acted in the Invasion.
Originally, the Polong was generated via the hate, anguish, sorrow, and thoughts of humans who lived, or died, during the war. These, along with the bloody battles occurring, acted as a massive catalyst.
Ionia's natural magics have seemingly limitless power, but without direction and purpose it can only do so much. When something like a sorcerer with ambition or desire can give the magic reason and purpose, suddenly this magic is so much more effective.
The catalyst formed from the Invasion gave direction to Ionia's innate power, forming an angry spirit, one whom was formed from all the suffering caused by Noxus's invasion. In addition, the spirit would be nurtured, encouraged, and fed by Ionian cultists, black art practitioners. Eventually, the Polong would become a fierce entity who could manifest by means other than physical existence.
Now the Polong begins its journey to Noxus, with a list of blood-bound Noxians and others to enact vengeance upon. For the first time it leaves the den in which it grew, empowered by dark cultists.