Perhaps the bad gal discovers she has a long - lost sister in the sequel. This sister has a completely different personality, being all good and kind. The bad gal has to decide whether to embrace this new family or push her away as she's used to being alone and self - reliant.
Another plot could be the bad gal trying to reform but her past keeps coming back to haunt her. Her old allies turn on her because they don't trust her new good - girl act, and she has to prove herself while also dealing with her inner demons.
It could be an old acquaintance who feels betrayed by the bad gal. Maybe someone she double - crossed in her previous adventures and now is back for revenge.
One idea could be exploring the backstory of a minor character from the game. For example, a random bandit who has a unique weapon and you could create a whole story about how they got it and their journey in the Borderlands. Another could be a story where the main characters from the game have to deal with a new, more powerful and mysterious enemy that has different motives compared to the existing ones in the game.
One idea could be exploring the backstory of a minor character from the Avatar world in the sequel fanfic. For example, a Na'vi who was on the fringes of the main events but has their own interesting journey. Another could be a story about the first human - Na'vi hybrid, dealing with identity issues and being a bridge between the two cultures. Or perhaps a fanfic that focuses on the restoration of a part of Pandora that was damaged during the events of the movie, showing how the Na'vi and any sympathetic humans work together to heal the land.
One idea could be that the male reader accidentally bumps into the shy gal in a crowded place like a bookstore. Their eyes meet briefly and she blushes and quickly looks away. The male reader is intrigued and tries to find ways to talk to her again. Another could be at a school event where the shy gal is participating but is really nervous. The male reader encourages her and that starts their connection.
Another plot could be about a mystery from the past that resurfaces. For example, a long - lost letter or a secret deal that was made during the original North and South era. This could bring the characters back together to solve the mystery and in the process, rekindle old relationships or create new tensions.
One idea could be exploring the aftermath of Daenerys' fall. Maybe a new leader rises from the ashes of King's Landing, someone unexpected like a former slave who learned a great deal from Dany's rule and tries to create a more just society. Another plot could involve the White Walkers not being completely defeated. A small group of them survived and are now plotting a new, more insidious attack on the Seven Kingdoms.
One idea could be exploring the backstories of the sisters more in - depth. Maybe each sister has a secret talent or a past trauma that hasn't been fully revealed in the original show. Another idea is to create an alternate universe where the sisters have different occupations but still maintain their strong bond. For example, one could be a famous artist, another a scientist, and they have to deal with the challenges of their new lives while still being there for each other.
Another idea is that Jesse and Amy go on a road trip. Along the way, they meet different people and have adventures. Maybe they encounter a group of musicians and end up joining them for a concert, which is something they've always wanted to do but never had the chance. This could strengthen their bond as friends and also help them discover new things about themselves.
Another appropriate fanfic idea is to have Gal Gadot's character time - travel. She could go back in time to meet the Amazons of old or forward in time to see the future of the world she's protecting. This would open up a world of exploration about her character's perspective on different eras and how she adapts to them.
One idea could be exploring the life of Renesmee as she grows up and discovers new powers. Another could be a story about the Volturi's reaction to the new vampire - human hybrid situation in the long term. Maybe also a plot where Jacob and Renesmee face some sort of external threat together.