The Girl's School on a Battleship. Meiji period. In the midst of the Russo-Japanese War, Shintaro Umakai was assigned to Amanohara Jogakuin as a teacher. The students in charge are five unique girls with different ages and growing environments. Shintaro decides to do his best as a teacher, even though he is puzzled by the unusual environment, such as the school building being in the basement. Meanwhile, a siren suddenly echoes in the school building.