Katras are a lie. They don't actually exist. Wanting to believe or not sure if you believe is not a sin.
Thanks guys, but this thread was not intended to be about whether katras, sin or God is "canon" or not.
My intention was to ask a question about the storyline of the movies and the motivation of the characters to help me make more sense of it so I can enjoy it more. Furthemore, suggested non-canon explanations are even welcome.