Nakua was originally a spider goddess that protected Sasanaki city. In the past, worshipers used to offer her human sacrifices, but the practice had since been declined. Since then, she moved to Hiro's school and devoured students that are lured there by a ghost story.
Despite the fact that Hime chose not to interfere with her activities, both Riza and Reiri decided to fight against her and drive her away from Hiro's school. Because of this, she decided to punish Hime and her servants by sending their villa into Ice Age in the past, but she was defeated once again.
In the manga, the shrine at the mansion has a stairway (in an alternate space) leading to a bridge she is building to connect the human world to the world of Evil Gods (also said to be the world of dreams.) When Hime asks her how long before the bridge is completed, she just smiles and says that they're rushing in the end, and that it has nothing to do with Phoenixes.