Teenage math whiz Kenji Koiso agrees to take a summer job at the Nagano hometown of his crush, Natsuki. When he arrives, he finds that her family have reunited to celebrate the 90th birthday of their matriarch. His job: pretend to be Natsuki's fiancé. Meanwhile, his attempt to solve a mathematical equation causes a parallel world's collision with Earth.
Balsa the spearwoman is a wandering warrior, who takes on the task of saving lives, in atonement for a past sin. On her journey, she happens to save a prince, and is tasked with becoming his bodyguard. And he is going to need one, for his own father, the emperor, wants him dead. Throughout the story, Balsa's past will come to light and they will uncover mysteries about Chagum's condition while developing a family-like relationship with each other and others.
A young pathologist seeks answers to the mysterious death of a friend and soon comes into contact with the same cursed videotape that caused the death of the friend's wife and son, which is haunted by the curse of Sadako, a relentless spirit.
