The Seijou Girls’ Academy Kendo Club is traveling to Shoushinji for a Summer training camp. Near there is an island, Urashima, where legend has it a demon extermination took place long ago.

They arrive around the time of a festival which honors a god that is worshipped by the people of Urashima; it celebrates the onitaiji and ensure another year of health for the people. Around the time of the festival, the weather around Urashima worsens and storms will come.

A few days into their training, Osanai Shouko finds a girl washed up on the shores near the location of the training camp. She cannot speak and doesn’t seem to know much about herself...

[From Wikipedia]