Since the dawn of time, spirits have existed with humans, living in either harmony or chaos within nature. They feed off the emotions of humans and the state of nature, growing stronger with every imbalance in the world. Some humans are marked permanently by spirits. It is believed to be a sign of a life full of misfortune. In return, however, they obtain heightened senses towards spirits. When unrest and hatred rise in the human world, the spirits burst out of a barrier separating the worlds to wreak havoc. Zuii lives in Unius, a formidable empire where a threat of a spirit burst looms over the divided civilization. She and her childhood friend Yuryna bonded over their spirit marks. But as the world of humans and spirits come closer to colliding, they join the Otherworld Defenders, a group dedicated to suppressing the spirits from taking over the world. While meeting new allies and learning more about the spirit world, they must come to terms with hidden secrets, dangerous changes, and a fate far greater than themselves.