I ALMOST passed on this spectacular anime series because I was initially put off by the main character at the beginning of the story. Boy am I glad I didn't and you shouldn't either!
At first, the set-up for Twelve Kingdoms is somewhat similar to Fushigi Yuugi: A rather annoying whiny schoolgirl and her friends get sucked into another world similar to ancient China. They can't get back home, they get separated, and undergo several harrowing encounters. But fortunately for us, the resemblance ends there.
The main protagonist Youko Nakajima develops from a very insecure and self conscious high school girl to a courageous and self-aware young monarch of the Kingdom of Kei. All the supporting characters including villains are complex and add to the multilayered storyline.
Twelve Kingdoms is a very detailed mythological fantasy that's like an Asian version of Lord of the Rings or Chronicles of Narnia without the religious undertones or allegory. The animation is gorgeous and the soundtrack specially the opening theme is epic in scope. It's just too bad the series is incomplete. Nevertheless this is one you should not to miss.