It can't be a coincidence that Icathia had two World Runes AND a connection to the Void.

In Ryze's lore his mentor forcibly took two World Runes from Icathia and destroyed the place.

Icathia is also deeply connected to the Void. I'd wager World Runes probably are the reason The Void can reach Valoran. From the Universe site's The Void page:

In places where the mystical barriers between Runeterra and the Void have been worn thin, the air feels charged, and fantastical occurrences are the norm. Rivers run with vibrant colors, flowers bloom with incredible perfumes, and living beings experience psychedelic visions and surges in magical power. For a time, such places are wondrous and brimming with miracles, but soon the landscape is twisted into new and deadly forms, and if the Void is able to consume enough biomass to survive, it can grow and evolve into something ferocious and terrifying.

Something else to note is that Jax was revealed to be an Icathian. That's why his skin is blue, and Kassadin's skin might be for a similar reason. Ryze is the third champion with such skin; blue skin could be a product of contact with World Runes or The Void, therefore.