This story would revolve around a reincarnated person. The character can be anything needed but would have needed to watch anime in a prior life. They would be forced to take a system that would connect them to the worst villains in different animes and works of fiction. The goal would be to turn the villains good and turn them into heroes.
The system would be forceful at first in order to make the character take the task and then become more of an afterthought. Just giving simple quests and rewards after.
Some different animes and their characters I have thought of are:
One Piece: Doflamingo, Blackbeard, Kaido, and Akainu
Naruto: Kaguya, Madara, and Orochimaru
Bleach: Aizen, Grimmjow, and Ulquiorra
Fairy Tail: Acnologia and Zeref
HxH: Hisoka and Meruem
Code Geass: Lelouch
These are some of the more popular antagonists in anime in mainstream anime, but any villain can be used. The main goal of the fanfic is to get a small to a medium-size group of villains to become a hero in their world and others.
Lots of bickering back and forth by the villains but they have to cooperate or else there will be punishments. Can start with one villain and slowly grow or can have a group all at once. Once they become a hero they have a choice of going back to their world or helping the main character help other villains change.
Any other questions or ideas are welcome in the comments.