I'm thinking of ideas for the next book of 'Upon a Star', and I'm stuck with a very big predicament. You could say it's a 'world-changing one'.
The story line I had was something like this (spoilers ahead):
Melody tricks Karyana into being her Surrogate, while her true goal is to reverse time and erase Medierth by changing the past. By stealing her power, breaking Asuna's mind and swaying Xelnos and Volkram to her side, she succeeds, trapping Karyana, Josephine, Lady Xera and others of Medierth in the real world, unable to emerge from their Surrogate bodies. The only ones who have broken free are Karyana (who is left trapped in the padded room of a mental institute) and a nihilistic Xelnos who has had enough of being manipulated.
On one side, Karyana's journey is to reclaim her powers, stolen by Melody, and try to find her role in the Old World - her current conflict is between saving it (losing Medierth and any chance of being with her family again) or destroying it (bringing Medierth back into existence, but making her as bad - if not worse - than Melody). On the other side, Xelnos, seeing the darker side of the world - OUR world - decides to destroy it, in some twisted form of justice.
Currently, Josephine - the one of this world and the only aid that Karyana and Lady Xera have - seems to have a similar point of view as Xelnos - that the world should burn and start over. Lady Xera, on the other hand, seems incredibly curious about the ways of the other world... and Karyana is torn apart from all the events.
Xelnos' plan? All the Black Eggs (nuclear weapons) in the world, and destroying everything wrong with the world, one Black Egg at the time.
Melody's plan? To be back with her children, and have 'the perfect family'. (...Looking back on Melody's plan, it reminds me of Victor's plan in 'Tales of Xillia 2'.)