After the "Gate" was reopened due to the activities of the Otaku self-defense official Youji Itami, the Japanese government mobilized the Self-Defense Forces, intending to further strengthen relations with the Special Region. Meanwhile, a special mission is ordered for Colonel Goro Etajima of the Maritime Self-Defense Force and the highly skilled chef Sergeant Hajime Tokushima, who were traveling around the Special Region on a survey mission, to recapture a kidnapped American Journalist. The two board an Oyashio-class submarine and set sail for the seas of the Isekai!