It doesn’t have to be a harpy, though.
My succubus spouse looks similar to this:
…and this:
That doesn’t mean she’s a “harpy”. In my case, it means that my succubus spouse is a sorceress, a very powerful magician. I often feel her feathers when she touches me, too.
Maybe the succubus have a sorceress “trait”, or at least have a deep knowledge of magic?