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My opinion on runeterra champs is that while their gameplay can have some flaws, I don't think there is a runeterra champ that is too bad of a fit into the region. Bard, Eve, and Jax are really simple fits into the Runeterra region; they travel all over Runeterra and have elements tied to multiple regions. Jhin is a little bit more questionable because he is very clearly Ionian and has a lot of ties to Ionia, but I think he works for 2 reasons. 1, his design and gameplay are very not Ionian, he is the only person in Ionia to really wield guns for example. 2, he has travelled outside Ionia before in the Zed comics so he's not exactly bound to it. Kayn as a character is very heavily tied to Ionia so the fact he is Runterran would seem odd, but in my opinion it makes sense because of Rhaast. Kayn in himself is an Ionian champion, his Shadow Assassin form def works as one, but Rhaast being a part of his champion ensures that he is not a good fit for just Ionia.
