I've updated my magical muse officer / gunslinger story, The Late Bird's Tale: A Tale of the Floating World, for your reading pleasure! Enjoy, folks!
https://www.scribblehub.com/series/496593/the-late-birds-tale-a-tale-of-the-floating-world/
The only time I've ever seen this executed well was in the Metal Gear Solid game series when they introduced Naked Snake (aka, Big Boss) in Metal Gear Solid 3, but they didn't scrap the original protagonist Solid Snake. They just shelved him for a time after lackluster reviews in Metal Gear Solid 2.
Worst thing I've ever done to a character was suicide/matricide; I had her either kill herself or kill her daughter. She chose to kill herself, so that her daughter could live; but when she killed herself, it turns out she was inhabiting her daughter's body, so her daughter killed her. It's...
For Villainess, Retry!, it's a little over 100 pages of typed notes; for Days of Blood and Roses, it's over 500 pages of typed notes. Besides character profiles and setting descriptions, there's links and notes on a lot of miscellaneous stuff.