In the future, humanity has been all but destroyed, only a small portion remains alive. Using the wisdom of older times, a group of winged girls, called angels, is created and is entrusted with the future of humanity. [Wikipedia](https://ja.wikipedia.org/wiki/%E7%B5%82%E6%9C%AB%E3%81%AE%E3%83%9E%E3%83%AA%E3%82%B9%E3%83%86%E3%83%A9)