Have you played Abyss? Best game ever. Hard to explain, but I will try anyway.
Aldrunt is a planet with two layers - The outer lands and the Qliphoth (I so butchered that spelling)
In the game's history the outer lands used to be in the Qliphoth, when a disaster came. The miasma (Poisonious gas) shrouded the outer lands, causing chaos, when Yulia Jue appeared. Using technology, she made the sephiroth trees to lift the islands up in the sky causing a crust called the outer lands.
However, later in the game, Luke Fon Fabre (Main character) found out that the miasma was appearing in a mining city called Akzeriuth. When he went to sort it out, Van (Luke's master & later villian) told him that if he demolished the sephiroth tree supporting Akzeriuth, the miasma would fade away. Earlier in his life, he has been kidnapped by the rivaling country called Malkuth, and that problem caused him to lose all memory of the past. Ever since he has been confined to the manor for his own safety, so he knows nothing about the outside world.
Without knowing it, he demolished the Sephiroth tree causing Akzeriuth to crumble and fall into the Qliphoth. Saved by Tear's fonic Hymn, he then realised the weight of what he had done and swore that he would change.
However, there is other things he should be thinking about.
It seems that all of the Sephiroth trees are connected, and now the whole world is at risk of collapsing. They lower the outer lands into the Qliphoth and realise they have to do something about the Miasma.
Jade has an answer, but nobody likes it.
Luke or Asch, a replica or an original, has to die, along with 10'000 7th Fonists.
Asch dosn't want to do it...
What if it is the only way?
Sorry about throwing that at you. But that is my fav game.