Gargantia on the Verdurous Planet OVA

Six months has passed since the battle with Kugel's fleet. Fleet that has been released from the tyranny of the machine caliber Striker is about to join the Gargantia fleet, and new people are coming onboard.Ledo, while working with salvage team, is gathering information about the old civilization. He seeks answers to questions why the mankind had left the Earth and what were the reasons of strife between human race and Hideous. Ledo had deepened his interest in archeology and explores the history of mankind. Meanwhile, Amy teaches her new messenger recruit, Leema, about her work. Leema is a member of the original Kugel's fleet and after its dismantling, she had begun a new life on Gargantia.

The story begins in the distant future in the far reaches of the galaxy. The Human Galactic Alliance has been constantly fighting for its survival against a grotesque race of beings called "Hidiaazu." During an intense battle, the young lieutenant Ledo and his humanoid mobile weapon Chamber are swallowed up into a distortion of time and space. Waking from his artificially induced hibernation, Ledo realizes that he has arrived on Earth, the planet on the lost frontier. On this planet that was completely flooded by the seas, people live in fleets of giant ships, salvaging relics from the seas' depths in order to survive. Ledo arrives on one of the fleets called Gargantia. With no knowledge of the planet's history or culture, he is forced to live alongside Amy, a 15-year-old girl who serves as a messenger aboard the Gargantia fleet. To Ledo, who has lived a life where he knows nothing but fighting, these days of peace continue to surprise him.

In the near future, Earth is at war with aliens called Worms. The war leaves the population of Earth decimated, with young men the main casualties. The Worms were beaten back but their re-emergence heralds the creation of a mecha unit called the Sonic Divers, piloted by 3 young girls to counter this threat.

For 200 years they lay deep beneath the earth or silent on the ocean bed. Now two opposing armies race to unearth these massive engines of war, devastating weapons known as Decimators. As more of these vast robots are reactivated, the world moves ever closer to another all-out war, drawing innocent victims into the deadly conflict.