When you look up at the sky, what do you see? A blue sky? Freedom? A hopeful future? The people of Tokyo see none of these. Instead, an ominous alien mothership looms overhead, engulfing the city skyscape. Three years ago, they came. The arrival of the "Invaders" sparked the greatest war humanity had ever faced—one that threatened to end the world. The Japanese government scrambled to fight the Invaders. Weapons were mass-produced, sparking controversy and pacifist movements. That day, everything changed. And yet, nothing has changed. Kadode Koyama and Ouran Nakagawa live their final days like they always have: going to school, playing with friends, and doing what any carefree high school girl would do. As they grow up, they come to learn what it truly means to be an adult, in a world where adults seem to be demons who only deceive and destroy. They come to learn the real threat to humanity is not the Invaders, but humanity itself.

The year is 20XX. The ninja, who once forged the history of Japan, were scattered across the country during the Meiji Restoration. As these ninja mingled with the other clans, their bloodline thinned, and they gradually faded from sight. The descendants of these ninja clans, seeking to preserve their heritage, formed the WNA (World Ninja Association) in the hope of carrying on their legacy. And so it was that the WNA succeeded in developing Ninja-Gum, an art which could summon forth the strength of the Shinobi. And yet creating the most powerful Ninja-Gum requires the strongest of ninja DNA. So it was that the Ninjala Tournament was held, that the mightiest of all ninjas could be found...

In the near future, a sudden and unexplained sea rise has left much of human civilization underwater. Ikaruga Natsuki, a boy who lost his mother and his leg in an accident some years earlier, returns disillusioned from a harsh life in the big city to find his old countryside home half-swallowed by the sea. Left without a family, all he has to his name is the ship and submarine left to him by his oceanologist grandmother, and her debts. His only hope to restore the dreams for the future that he has lost is to take up an opportunity presented to him by the suspicious debt collector Catherine. They set sail to search the sunken ruins of his grandmother's laboratory in order to find a treasure rumor says she left there. But what they find is not riches or jewels; it is a strange girl lying asleep in a coffin at the bottom of the sea. Atri. Atri is a robot, but her appearance and her wealth of emotions would fool anyone into thinking she's a living, breathing human being. In gratitude for being salvaged, she makes a declaration to Natsuki: "I want to fulfill my master's final order. Until I do, I'll be your leg!" In a little town slowly being enveloped by the ocean, an unforgettable summer is about to begin for this boy and this mysterious robot girl...

The night of a family birthday party. The mother is tired from work and wants to drink a beer as soon as possible. The father is fidgety and keeps an eye on the clock. A little girl is excited about the sumptuous meal and runs around the house. The intercom rings. There, a "new family member" is standing there... (Source: Official site, translated)