Rek'Sai is a terrifying, unstoppable beast!
What exactly would stop the folks from Shurima hiring Zaun or Piltover from coming in with a couple airships, dropping a seismic thumper on the ground, and then blowing Rek into a steaming heap of gibblets as soon as she surfaces?
She's a big (megalodon sized if the video is to be believed) scary animal. Neat.
Large predators aren't a threat to any sufficiently technologically advanced civilization. There's a reason why most of them around the world are extinct or endangered. It's because tools and intelligence trump bestial ferocity pretty handily. Now, if Rek were Godzilla sized like a few of the nasty folks from the Cthulhu Mythos I can understand this not working. If she utterly defied conventional physical laws, yeah, that would make problems. But the route Riot seems to be taking with the Void now is that it's just a spooky purple universe and Rek happens to be a (large) example of the wildlife from there.
So that leaves me wondering, why is this critter a champion, exactly? Why is she a threat to anyone other than some poor losers who don't have so much as a pointy stick to defend themselves?
. If they don't have the resources to handle one person I doubt they have enough to send an expedition to a desert which is like 1/4 the entire continent (if accounting Urtisan and Fyrone Flats). Also creatures that are underground that have a large network of tunnels are hard as hell to locate and find. A good example of this is when the US tries to find terrorists located in mountain caves, they use satellite imaging and constant drone monitoring and it still takes them years to find the terrorists and Im pretty sure that Piltover doesn't have satellites or drones to monitor such a vast area so it would take them even longer than that to get a reasonable finding let alone kill Rek'Sai.
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