I first saw Isogashii on images of the Hyakki Yagyo Emaki. I can’t say what drew me to him originally. Something in the face, I think. I needed a charming sort of ugliness for my main yokai in The Changing Things, and when I saw Isogashii, I knew he was the one.
Well, it turned out I couldn’t have made a worse choice, research-wise. Very little is known about this yokai and there seem to be no associated folk tales as far as I can tell. It was nice to have liberties, but I has hoping for some foundation to draw from.