I'm of two minds on the whole otherkin thing.
On one hand, it seems to be a way for your typical misunderstood teenagers and immature young adults to be special and unique (just like everyone else). The propensity to claim fantasy spirits like elves and lycans (yes, lycans, like in Underworld), as well as other things specifically from TV shows or movies, kinda reinforces this thought for me. I got acquainted with someone who believed themselves to be a dragon-vampire-tiger otherkin. To me he mostly seemed like a young man with his head in the clouds and an untreated mental illness. And coincidentally, a fascination with dragons, vampires, and tigers. I have met others who seemed sane and stable, but claimed to be fantastical otherkin... so I just don't know.
On the other hand, I have met two people in my life that make me think there just might be something to the basic premise of otherkin. One was a woman who was a bit of a recluse. I was a kid at the time, but looking back she was very bird-like. Always fluttered around, very skittish, thin, tiny frame, very quick almost darting movements. And strangely, birds came to her house to die. She held them til they passed and after they were dead she often made things out of their corpses (which is slightly less gross than it sounds). She stuffed some, pulled feathers and sold them, and she made tiny panflutes from their bones.
The other person is a man who raises orphaned and injured wolves. He's great at his job, but he's really bad at normal social interaction. He believes he is wolf otherkin, and that's why he chose to work with wolves. I got the pleasure of seeing him begin integrating a pair of captured wolves into the pack he works with. It was amazing and fascinating and really strange, all at once. He is dominant to the pack he works with... and the pack ranges from 5-10 at any given time. They could literally tear him apart, but they don't. He even fights dominance challenges as if he really is the alpha of the pack. Wolves just seem to accept he is one of them.
So basically, I think the fairy-dragon-werewolve s are a load of crap, but there are things I cannot feasibly explain that certainly fall into the premise of otherkin.