How is Kayne not creating copyright issues?

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So the bible has a character that consumes soul motes for power? I need to read this thing. Sounds cool.

Not really. "Cain" as described in the Bible, was the first-born of Adam and Eve who murdered his brother, as the world's first murderer or something, who was then banished by God from his country.

The name is sometimes borrowed, but not always the theme and setting entirely. In the case of League, "Kayn" is merely a nod to the biblical reference given that he has a somewhat relate-able theme (given that he and his inner demon Rhaast have to kill each other and one of them has to die as the game progresses).