Only on this island

Sora went into the sea on her birthday because her fiance put her there, and she drowned. She wakes on Hongmido, a small island far from anywhere, and works out fairly quickly that she is dead and that nobody can see her. One person can. Haneul is a young shaman living on the island, and through him she gets a human body back, on loan and not permanently. Her real body still exists, and the way to get it back is Guihonsik, an old resurrection rite that they are not supposed to perform. They begin preparing it. Her fiance is not finished with her either; he wants her gone completely, in a way that leaves nothing to come back to, and he starts moving toward the island. There is also something already on Hongmido, an evil spirit that has been there a long time and does not want the rite carried out. Between the two of them, Sora and Haneul are pushed to a point where the danger is no longer death but the soul being destroyed outright, which would end any chance of the ritual working.