At the end of WOR Seth is given a black Shardblade by Nin and is sent to bring justice to the leaders of the Shin. When he picks up the blade: "Hello, a cheerful voice said in his mind. Would you like to destroy some evil today?"
This idea of a higher power influencing the characters through a voice in their head seems eerily similar to Mistborn's Ruin. Could this be Odium or another God guiding Seth?