Just hear me out on this...

Varus. One of many champions who have had very little publicity as of late, particularly with regards to lore. I know, writing lore and make sure it's both high-quality and cohesive takes time. Riot has only recently started actively putting out lore, so it will take time for them to give all nigh-140 champions their time in the spotlight. Riot is also trying to tie things together, and stop leaving out loose-hanging threads and unrelated aspects. Sooooo I had an idea.

Corrupting. Consuming. Eldritch. Purple.

We know that the Void comes into Runeterra through portals or rifts. Rifts with evidently require the magic equivalent of a nuke in order to close. I would assume that even in a place as magically enriched as Ionia, such power is not easy to come by. So perhaps Varus' powers, the corruption he has doomed himself to for the sake of vengeance, could be made to originate from the Void? I mean he certainly wouldn't be the first, would he?