Key Zero: Children's Lullaby:

Little field mice run around in the dry grass. They eat their wheat and grain while miles away the angels suffer in the Fallen City. The lucky little field mice don't know about the hell that they live in front of. They just eat, play, and breed in peace.

But once in a while, the mice cross the line into the Fallen City.

There is no grass there. Black as far as the eye can see. The ground becomes so rocky that their little feet start to hurt. The thin air hurts the little curious mouse in the city. They have to slow down to conserve air. The scent is usually enough to drive them back. Yet, some of them don't leave right away. The slower and slower they walk, the more the little mice feel the pain in their feet. It gets to the point that they cannot move anymore.

The air is so cold and dry, that the sugar in their little bodies starts to harden. Sweat breaks all over their little bodies. Their stomachs start to turn in pain.

I don't want to be here anymore!, they think to themselves. The mice are always lucky to run away before they die. They fleet to the dry grass outside of the city. The clean air always welcomes them back. The mice enjoy their grass and morning dew from the tree that shades them from the dim sun in the scattered sky.

The angels, on the other hand, are not as lucky to escape. They cannot leave the Fallen City. Their wings have been torn off of their backs and invisible chains on their ankles keep them within the grounds. There are nine circles before any unlucky soul makes it to the tower.

The angels trapped in the tower seem to have it better than those on the outside. Yet, this is only on the outside. Sure, they are taken care of inside, but not without a price. That price depends on the master that owns them. Most of the time it turns out to be rather humiliating on the angel's part.

So who owns this tower? No one really remembers anymore. The masters in the tower don't even know who their boss is. Maybe this is why there is no regulation in the city and the tower.

But, why are the angels there? How do they end up in that Hell? Who made the tower? Did this city used to be beautiful? How did it break down into decay? How long had it been like this? Does anyone even think about the Fallen City as the years go on? Does time even move in this place? The unanswered questions are rather endless. Yet, everyone that has not been taken by the despair around them tries to find the answers around them. Some of them even try to escape in vain. However, there is one clue that they angels fail to notice. The whole fallen city has something to do with the core of the Wasteland.