Hundreds of years after the 20th century, nature and the ecosystem have been devastated due to use of nuclear and biological weapons. Most of the Earth has been contaminated and is collapsing into ruin, and a great majority of plants and animals are now extinct. The world heads to the "Big Six," the sixth mass extinction event. Humanity built cities in the sky, migrating the endangered species of animals and plants there. Over many years, the animals evolved in these isolated cities. With artificial genetic crossbreeding, they acquire language, bipedality, and build a life and civilization for themselves free from want. No one thinks of the world below any longer. One day, a single plant seed wanders into one of the sky cities, and the children Kui, Hiruma, and Root discover it. Unable to resist the temptation to look into the world outside, they decide to undertake an adventure to the outside world, unknowing that once they set foot on the ground, they will never be able to return.
It is in most senses your typical mediocre, 1-episode kids OVA, but I did think that it did well in 1 way: It really gives off a sense of the puniness of the story being told. The implied universe they're in is gigantic and foreign, and it doesn't stop to explain anything to them or the viewer. In a sense, the characters are as brand new to the universe as the viewer is.
In the end it shows a completely new environment from the rest of the episode, and then a far off electrical storm, and offers absolutely no explanation. There was utterly no reason for
it to be there, and I found that kind of interesting. They throw you into what could be a vast and fascinating universe, just to shamelessly tear you from it after 20 minutes, with no chance of returning. I felt it was a good change from the norm, where the characters are the center of the universe and everything has to make sense to the viewer. This feeling is what I love(and hate) about this kind of 1-episode OVA. A whole universe blooms before your eyes, just to shrivel and die after 1 episode. Maybe I'm just trying too hard to find good parts to justify a bad anime. I don't regret watching it, though.