Often, there are the victims or potential victims of Jeff. They might be ordinary people in the neighborhood who start to notice strange things going on and suspect Jeff. Another common character could be a detective or a police officer who is trying to solve the mystery of the killings and might eventually cross paths with the little sister.
Well, one common character is a female love interest. She could be a strong - willed person who is initially scared of Jeff but then gradually falls in love with him. There might also be a sidekick - type character for Jeff, someone who has known him for a while and tries to warn the love interest about Jeff's true nature. And in some fanfictions, there could be a detective - like character who is trying to solve the mystery of Jeff's killings while also getting involved in the love story. This character might be suspicious of the relationship between Jeff and the love interest and tries to break them up for the sake of safety.
One common theme is family. It often explores the relationship between Jeff and his sister in the context of his transformation into a killer. Another theme could be protection, like how the sister might try to protect Jeff or vice versa. Also, there's the theme of horror and how she copes with the terrifying world Jeff has become a part of.
Yes, there are some interesting ones. You can find them on various fanfiction websites. Just search for 'Jeff the Killer Little Sister fanfiction' and you'll get a list. Some might focus on the relationship between Jeff and his little sister, while others could create unique storylines around her character.
There could be his victims. They might not recognize him at first when he turns into a girl and he could use this to get closer to them. Another character could be a mysterious figure who either caused the transformation or is trying to help Jeff reverse it.
A lot of the fanfiction focuses on the power struggle. Jeff has his own dark power, and sometimes his sister also has some sort of power, and there is a struggle between them in terms of who is more powerful and how that power is used. Also, the theme of protection is there. The sister may try to protect others from Jeff or protect Jeff from himself.
Well, a plotline might involve the little sister being in a constant struggle between her loyalty to Jeff and her own sense of right and wrong. She might also be hunted by the same people who are after Jeff, which would add a lot of tension to the story. And she could form an unlikely alliance with someone who initially wants to kill Jeff but then realizes she can be a force for good in the situation.
The main characters are Jeff the Killer and the little girl. Jeff, with his terrifying nature, and the little girl, who might be portrayed as either very brave or very naive. There could also be side characters such as the neighbors of the little girl who start to notice strange things happening around her since Jeff entered her life.
Sometimes, other killers or creepy characters from the same horror universe might make an appearance. They could either be allies or enemies of Jeff, adding more complexity to the story and the exploration of Jeff's insanity.
Well, Jeff the Killer is surely a main character. There could also be a made - up character who is the other half involved in the pregnancy. And perhaps there are some side characters like friends or foes of Jeff who play important roles in how the pregnancy unfolds and how they react to it.
A rather unique 'Jeff the Killer Baby Sister' fanfiction I've read is about her being in a parallel world where Jeff never became a killer. She experiences a completely different life with her brother, but then things start to change when elements from their real world start to seep into this parallel world. It's a long and detailed fanfiction that really dives deep into their relationship.