- Vanquished power
- Victorious enemy OR Messenger
Plot: Vanquished power falls from its place after being defeated by Victorious enemy OR being informed of such defeat by Messenger.
The point of Disaster is that it changes the world of the Elements. It can be big scale, like the fall of a kingdom, or small like a divorce.
The intensity increases when the disaster in unexpected: the kingdom seemed to be winning the war, the enemies seemed weaker, the spouses seem to be all right.
The Vanquished Power has to adapt its life to its new circumstances. It's a reactive element.
PCs as Vanquished Power
If the PCs couldn't avoid the Disaster, this story is going to make them feel desire of revenge, and that means they need somebody to take revenge upon. In literature is all right to get an earthquake or a volcano eruption, destroy a city and show what the characters feel and do while mourning their loss. In an RPG, though, is better to have a NPC to blame - otherwise, the players could blame it on the GM - so the disaster should be an unexpected defeat.
The PCs need not to have being fighting against the Enemy. While the party was recovering an ancient artifact, their recurring enemy attacked the town they grew up and torched it. When the players return, they see a few survivors, mostly children or old people, and adult dead bodies. They cry, speaking about the forces of their enemy. The PCs need first to take care of their people, and then track their enemy and take revenge for its actions.
If the PCs could have avoided the Disaster, this story is of the consequences of their failure. In that case the try to avoid the disaster was in the past sessions. Maybe the first sessions were clues for them to start preparing action and they didn't or didn't get them, but they need to had chances to avoid the damage to not feel unjustly beaten.
In some disasters you can have a Victorious Enemy, somebody to blame, to take revenge on, to hate, all that.
PCs as Victorious Enemy
The point of Disaster is that the PCs care for the people affected by the disaster, so how are you going to make them care about the negative consequences they brought while winning, without making them feel remorse? Maybe if those consequences are not purely because of the PCs. The PCs are mercenaries hired by a count in a war against a neighbor. After the main battle, the army marches over the loser's lands, pillaging, butchering and raping civilians. The PCs are horrified they brought this upon innocents and try for it not to happen, but there are too many cases for them to stop them all.
In any case, the Victorious Enemy is who brings the great damage over others, and not many players will feel right doing that.
Both a defeat and a natural disaster may need a messenger to really get the Disaster feeling, although both may be their own messenger.
The Messenger talks about the Disaster, but with it comes the chance to avoid a greater damage. If a city has fallen or an army has been defeated, the Messenger can alert home and let them evacuate before the Victorious Enemy arrives.
If it was a natural disaster, then the loss needs to affect the people the Messenger talks to. A king sent his army to a quick campaign. However, a plague killed most of it, only a few soldiers (Messenger) were not affected, able to return and tell about the loss of almost all the army. Now that the king has no army, neighboring kingdoms may attack them. Maybe the king just came back from a negotiation with one of those kingdoms. A negotiation that wasn't good and that only the implicit threat of the king's army stopped the ambition of the neighboring king.
A Disaster naturally develops into a Falling Prey of Cruelty/Misfortune story, with the Vanquished Power being the Unfortunate and, if there is a Victorious Power, it becomes the Master.
If the PCs are in the losing end, maybe there's no need to play such story if they want to go straight to Ambition, Obtaining, Daring Enterprise or Conspiracy.
Maybe a Sacrifice is required for the situation not to worsen. For instance, a enemy army may have taken the PCs fortress, but they are willing to forgive the PCs' subjects if they surrender and publicly give up any right they had to it.