Why Each Character Has Joined the Cult on American Horror Story (So Far)

Kai seduces Harrison (both physically and intellectually) at the gym where he's a personal trainer. It's clear that Harrison is kind of a doormat to everyone, especially the head hotshot trainer who works as his superior. Kai inspires Harrison to stick up for himself, which means killing his boss and moving on with his life. It's this sense of importance and value that Harrison covets the most.