Otome Game Afterstory
After the end of the main story, the hero slays the demon lord, and the party goes all their own ways happily ever after... or so it goes. Except is it really a happy ending?
This story takes the perspective of the Mary Sue heroine after the epilogue. She is married to the hero, who is now an alcoholic war veteran who recently received the title of duke. Despite an exterior of nominally looking like a happy couple, the hero actually has a lot of darkness brewing inside of him. Specifically, after killing the demon lord, he absorbed a lot of the darkness, and those dark aspects have started to manifest in twisted ways...
Specially, the hero has a dungeon and abuses his wife (the heroine) every night, and basically the heroine is trapped in this hell where the hero is gradually becoming more and more evil... In fact, he's basically a male yandere...
The story begins after a particularly bad night, when the heroine suddenly begins to partially recover her memories from her past life due to her serious injuries. She realizes that this setting is identical to an otome game that she once played, except it's already past the ending. The heroine already reached the "Happy End", yet somehow things became twisted and three years later it's looking very miserable...
The heroine considers going to some of her "friends" (former classmates and party members), but everywhere she turns, things are looking more and more twisted and hopeless. Somehow, everyone that she used to care about became increasingly nightmarish (i.e. killing cats in the backyard shed, becoming a tyrant ruler), and the heroine slowly realizes that anyone involved in killing the Demon Lord (all of her friends) received a curse that corrupts them with evil. The heroine wasn't effected as badly because her past life memories are stabilizing her.
As the entire kingdom gradually turns dark, revolution (from unhappy peasants) and war/invaders (from a foreign country) looms over the kingdom.
The heroine is quickly presented with a choice: Should she betray her former friends (who would be executed/lynched by the peasants/invaders)?
However, the heroine clings to a desperate hope that she can save her friends from the curse of Darkness. She allies herself with her friends in the nobility by pretending to be a villainess (while being abused by her yandere husband at night), does atrocious things to the peasants/invaders, while meanwhile attempting to research the Darkness in the former Demon Lord's castle in a vain attempt to undo the evil spell.
Specifically, in the Demon Lord's study, the heroine finds a book that seems to contain a Dark Magic recipe that will undo the Darkness curse. The steps to activate the spell are clearly outlined in the book, but it involves doing three very bad things: (A) killing someone precious from each of the victims and putting their bones in a potion, (B) ten thousand innocent souls and imbuing all the evil, and (C) signing a contract with the God of the Underworld promising to be the new Demon Lord's succsesor.
Fast forward a bit more and the heroine => OP villainess with a cast of evil friends who are her allies.
She secretly accomplishes all of these steps and manages to break the curse on her friends/husband.
When they wake up from their corrupted state of evil, they are horrified by what they've done to their kingdom. Then they realize that the heroine has become the new Demon Lord, so they promptly kill her. They all surrender themselves to the revolutionaries, and after hiding away their respective children as orphans (a bunch of them were married and have kids... some of them grew up kind of twisted), they accept being executed as the instigators of the evil nightmare regime. They all die. The end!
