Just Persona 5 things

No plan survives enemy contact.

Well, worded around properly for the topic should be "No idea survives outlining/writing." And while I know this may not be the case for everyone, it is my method of planing and how it goes horribly wrong.

To explain properly, the way I handle a story idea is pretty simple, and I'll use my Saber Alter/Irisviel thingy that I am writing as an example:

1. Someone makes certain comment/I read something interesting/I watch certain thing/Playing videogames and then an idea pops up. My mind starts running all the possible opportunities that comes from this. In this case is both Fate/Zero and RB's fic that dealt with Saber/Iri fluff. My mind then thinks about the possibility and lands on Saber and Iri surviving the 4th War.
2. Then goes the how I would approach it. 1st person narration, 3rd person narration, lineal narration, non-lineal narration, etc. Since it's something silly and not serious at this point, I go with lineal-3rd person narration.
3. Then goes the events that should happen within the story. Since in this case its fluff, I decide on a random thing and leave it at that.
4. Now comes the horrible part where the idea becomes corrupted (Pun intented). See instead of accepting the idea as it is and moving on, my mind reels on the way it could work on canon. If there is no way then it immediately goes to an AU setting and drops the issue. However if there is a way, well refer to the next step. There should be no way that Saber and Iris could survive the 4th grail unless Iris doesn't get killed by Kotomine which would led to Kiritsugu finding him early. Maybe. And Saber could only keep on living via AM but then Gil would have to be defeated and Saber to reject her wish. But then what if she sees the fire and, since she is already hesitating to get her wish and she hasn't dwelled on her "I should not have been king" monologue could she do that? Maybe.
5. Now it its an AU, its just choosing a setting and voila, idea formed. It rarely is that easy. If it can be kept in canon then there is the decision on what I am going to focus on, and if the original idea still holds weight or it should be discarded. In this case, one character has changed. So I should give more focus to her. And wait, why not focus the entire thing on her, to show how different she is now. Yeah that sounds interesting-er, good bye fluff, you had a great possibility.
6. And then there is the integration on canon and how many ripples it would form. Sometimes some things in both backstory and "frontstory" are changed. In this case Saber Alter is the one that finds Shirou. Because of this, Shirou's distortion is created differently and, as such, will be different.
7. The final touches, scenes, focus, time period and details are decided. Most of point 4 is kept intact in essence but for it to make sense is changed while being writing. Spoilers, spoiler, spoilers.
8. And with that, the writing starts. Which should be covered later.