Sakaki Mio is a completely ordinary high school student.

...However, perhaps having been influenced by her grandmother who had raised her, Mio can be somewhat old-fashioned. As a result, she's often isolated by girls of the same generation. She becomes too focused on others' feelings, and becomes unable to open her mouth. Mio has been told that she "has a good intuition", but she's never really paid much attention to those words.

One evening, she got spirited away during the twilight into the realm of the dead and becomes lost in a secluded country of perpetual night. A world in which beings that are non-existent in the world of the living come and go, Mio meets various "lives".

The young girl was invited into a chinju (Shinto tutelary god) school, in which its attendees protect the world order by hunting down youkai (Japanese ghosts, demons and other supernatural creatures) that disturb the peace within the realm of the dead. Mio then gets embroiled in an incident that shakes up both the world of the living and the realm of the dead.

[Translation of official website story summary.]