A question

The word Makai means "demon world" and the word Jyujinkai means "man-beast world". The story makes a mistake by saying that Makai and Jyujinkai means the race just as well as the dimension. In actuality, demons are generally called Majin in Japanese and man-beasts are generally called Jyujin in Japanese. As to whether this is all from any real Japanese mythology, I would have to go with what the creator Toshio Maeda has said. The idea of Majin and Jyujin has existed in Japanese mythology for thousands of years. Legend of the Overfiend simply draws on various types of Japanese mythologies and puts them all together in one big, fat, convoluted story. As for the particular creatures, the legend of the Chojin and the chaos involved in the story's main plot, no, that's all made up by Mr. Maeda himself. But I'm sure if you research some Japanese mythology, you'll find a lot of references to certain creatures that resemble the monsters in Urotsukidoji, such as the cat-like humanoids and the reptile-like demons. If you watch the anime called Vampire Hunter, which is based on the video game Darkstalkers, they call the vampire lord Demetri Romanoff and the demon queen Morrigan Aensland both Majin from Makai. And the werecat Felecia and the werewolf John Talbain are both called Jyujin from Jyujinkai. It's pretty common in Japanese mythologies.