Part of why it was always such a challenge to figure out an episode with a succubus or a siren was that with two male leads it’s very obvious very quickly where it’s going. I remember breaking that out for the first time and it only took me fifteen minutes because it’s very clear that the siren is going to becone interested in one of the boys. So you need a twist, you need someone that you thonk is the siren, which we had in Cara, that sleeps with one of the brothers, and the other brother needs to get involved with someone you don’t suspect at all. Obviously the relationship between Sam and Dean is central to our show but we’ve been building this rift between Sam and Dean all season, so that led to the idea of having this young male character that sort of idolizes Dean and does all the cool stuff that Sam won’t do, and that’s Dean’s perfect mate. Plus, it was just a really good way to hide the siren.