Though her trip to Okinawa was supposed to be a lovely excursion to the seaside, college student Kaori Sawahara finds that it is anything but when a horrifying menace emerges from the watery depths. A strange mechanism has taken control of the sea creatures, granting them legs and sending them on land to attack anything in their way. Kaori and her friends—the lustful Erika and the reserved Aki—find themselves caught up in this onslaught, made worse by the creatures' rotting stench of death. Surviving the first assault, Kaori tries to contact her fiancé Tadashi in Tokyo. However, the call is cut short in what sounds like another fish attack. Fearing for his safety, Kaori leaves for Tokyo. With Erika and Aki contending with the attacks in Okinawa, Kaori rushes to find Tadashi, unaware that the crisis has only just begun.

In C.E.75, the fighting still continues. There are independence movements, and aggression by Blue Cosmos... In order to calm the situation, a global peace monitoring agency called COMPASS is established, with Lacus as its first president. As members of COMPASS, Kira and his comrades intervene into various regional battles. Then a newly established nation called Foundation proposes a joint operation against a Blue Cosmos stronghold.

In a world where humanoid armored weapons known as "Titatonostrider" ("TS" for short) are used in warfare, troops from various countries converge on the island of Oahu, Hawaii, including Ao Isami of the Japan Ground Self-Defense Force and Lewis Smith of the United States Marine Corps. Isami and Smith cross paths during battle, but suddenly, their teams are attacked by an unknown enemy, scattering soldiers and sending their forces into disarray. In order to save their friends and survive on the deadly battlefield, they must fight with every ounce of courage and pride that they can muster.

Three new OVAs of Futari Ecchi released as standard DVDs and as part of a Premium DVD Box containing all seven OVAs of the series.