You many answer, well, the voidlings just roam Runeterra and do what they please. But... here's the problem. Rek'sai is said to have influenced Shuriman Culture, meaning they could be here for longer than the other void inhabitants. And unlike the others, they came as a species.... So, anyone have any bright ideas?
It seems like In Runeterra's specific places, dimensional bound is stronger than normally. And Icathia is a really unique place that had an immense rift (with the chance of the biggest rift that Runeterra ever seen) in the past for at least once.
So, In Ancient Shurima, Ascended and Void fought and made a horrific war, many of them died, Ascended nearly went to extinction but they won. Maybe after Void's loss, Xer'Sai followed their survival instincts as primitive beings, ran away and made Shurima their new home.
That's my theory.
They arrived in the days of ancient Shurima when Icathia was still a major thing, but presumably they've always been a species from the void. The boundaries between Runeterra and the Void are pretty weak around Icathia so void invasions are very possible.
She came around when Icathia was major city most likely. She is the Queen of the Xer'sai so it is most likely that she gave birth to many, MANY of the Xer'sai inhabiting Shurima if the Xer'sai are anything like insects in this regard.
She was a random voidling that got left behind during the major Void incursion long ago. In the mean time she got huge and spawned a bunch of smaller bugs.
Maybe there's been more than one Rek'Sai. Like a bee. The old Queen dies, a worker becomes new Queen.
