While I never feel you should beat your audience over the head with exposition, I felt this was poorly done. I never even knew there were 13 races. Were these ones in particular just adapted into different kaijin?Wolfren
Mermaid - female Mermen
Ghost
Goblin
Gigant - cyclops/yetis
Hobbits
There is quite a lot of information in the Kiva entry for the japanese language wiki.
I didn't even know about the Thirteen Demon Races until I read it online after watching the series. One thing I've been wondering though, what race was Tatsulot? Or is he in that weird category with Sagarc where he's another one of the Races, but not specified which one?