With the Gate open again, Japan's government wants sole control of the passage and keeps sending the Self-Defense Forces into the Special Region on political and mapping missions meant to build peaceful ties with its people. Captain Edajima Goro of the Maritime Self-Defense Force and his subordinate Tokushima Hajime, a former chef, travel between its nations on diplomatic and survey work. Their duties change when they are ordered to rescue an American journalist taken captive on an island in the Blue Sea. Aboard the submarine Kitashio, they find those waters in upheaval, with island nations and pirates fighting for control. The season mixes action, adventure and drama with fantasy.