Based off World's End Umbrella by Hatsune Miku.

The Great Umbrella, the only thing standing between life, and the extinction of the human race. The umbrella stands over a small section of the planet, protecting the small amount of remining survivors. That small amount, being only 700 people. About 350 male, 350 female. 500 adults, 200 children.

The Umbrella is a large dome-like structure that holds in oxygen for the humans to breathe, ever since the catastrophe of X890, When almost all but 2% of the oxygen was sucked out of Earthland through a tear in the ozone layer. Even after scientists were able to repair the gash using a chemical reaction with lightning, the oxygen was still gone, and peole everywhere were slowly dying.

Humans were being erased from the page of life.

Scientists and architects began to work on what is now known as "The Umbrella Tower", a large dome that would protect the rest of civilization. It was completed in only two weeks, but by then, 99% of earthland's population was gone. Dead bodies lay in the streets, like something out of an apocolypse movie. Only 700 people left alive...seemed like a nightmare. Those remaining 700 were brought to the Umbrella, where they tried to continue living "normal" lives.

There were two children out of those two hundred who thought differently from the rest. Their names were Natsu, and Lucy. Both were only twelve years old, when this adventure took place.

This is their story, of that certain adventure.