Speaking of youkai, I had started reading a series called Rosario + Vampire. It involves a youkai high school, in which the main male characters end up their by accident. It is probably not the best manga out their, and it is typical supernatural, high school, harem story. Though a few of the characters caught my interest, and I have enjoyed the story. My favorite character is a snow woman called Mizore. I also like the main male character Tsukune, he is in love with a vampire girl with a split personality.
He had been taking her blood to save her and the other girls. It got the point where he was turned into a ghoul. It's not everyday that a guy will go that far to protect those he loves.
I also like the youngest character who is a witch, she is 11 years old. And wants to have a threesome with Tsukune and Moka the vampire. Something about that just hits my funny bone, the story will also self parody when dealing with manga. So I have enjoyed it, I have no idea if it is a good series or not.
The anime of it isn't so great either, I prefer the manga. But it is light hearted, and it has Mizore.