The protagonist is a girl who has been invited by some boys to spend a night telling ghost stories in an old shrine as a test of courage.
In the middle of the hundredth story, they discover a hidden door in the shrine. After descending an underground path, what they see at the end is...
Legend, a guardian deity, sacrifice.
They had thought this was all a forgotten old tale. But when the sacrificial markings are left on the girl's body, they are once again visited by the guardian deity.