Legend has it that a long time ago, humans had no shadows. This was the curse of Na Dasheng.
That's because the curse of Nada's old demon was broken by Prince Philip's kiss, the sleeping beauty woke up, and they lived happily ever after.
The furious Nadasheng cast a nightmare spell on the entire city, and the other half of human beings, the shadow, was abruptly stripped away.
"Imperfect humans don't deserve such perfect love!"
From then on, even though people there fell in love, they could never be together.