The Girl from the Other Side: Siúil, A Rún

The Girl from the Other Side: Siúil, A Rún summary:

"It is a story full of sadness. From now let's recite a slow and beautiful story from long ago."

Once, from the conflict between the Black God and the White God, two countries were born, separated by a long wall. One side of the wall was “inside,” where normal people under the White God lived; the other side was “outside,” where those who were cursed under the Black God lived.

Shiva, a young girl who loves to stroll about in the countryside, lives in a vacant village with her guardian, a wendigo-like gentleman that she calls her "Teacher". He forbids her from going outside so she won't be cursed, but Shiva's curiosity makes her yearn for the outside world. What is this curse about, and how did Shiva come to be with her Teacher?