Found some info on the mythology of Wanyuudou and decided to share it with you. My sister had told me about it earlier, but I decided to go dig it up myself and I found some interesting stuff. =)

Wanyuudou / Wanyūdō

Literally in Japanese 輪入道 (Wheel; entrance; road). According to Wikipedia, Jigoku Shoujo seems … fairly accurate at describing him. Wanyuudou is a well-known youkai [http://upload.wikimedia.org/wikipedia/commons/5/5c/SekienWanyudo.jpg
http://www.monstropedia.org/images/c/c3/Wanyudo.jpg

MYTH
According to folklore, he is the condemned soul of a tyrant daimyo, who had his victims drawn on the back of an oxcart. Guardian of the gates of hell, he wanders on the road between the underworld and this world, anyone who sees him (or, rather, gets close enough to him), he drags along with him to hell.

SOURCES
http://en.wikipedia.org/wiki/Wany%C5%ABd%C5%8D
http://www.monstropedia.org/index.php?title=Wanyudo

NOTE: Sorry I haven’t had more, I’ve been trying to find about the art in the Jigoku Shoujo opening since that looks fairly old-fashioned, and interesting, but I’ve had an exam coming up and I’ll have more time to blog now. Hehe.