Obviously, Killmonger is likely to be one of the main characters. But without more information, it's hard to say who else might be. There could be characters from his family, friends or foes in the story of the visual novel.
In such a fanfiction, Naruto's character development would likely be very different. As a girl, she might face different challenges and discrimination. Maybe she would have to prove herself even more in the male - dominated ninja society. Also, the fanfiction could explore how her new identity affects her jutsu usage. For instance, she might develop new techniques that are more in line with her feminine side or adapt existing ones in a different way.
According to my knowledge, Fanka is a fictional country created by a man named Fanka. His work exposed the dark side of the country's society and depicted a group of people who fought against social injustice.
Ramonda, Shuri's mother, can also be a significant character. Her wisdom and experience can play a role in the fanfictions. Maybe she tries to mediate between Shuri and Killmonger, or she has some secret knowledge that can help Shuri deal with Killmonger. Her presence can add a touch of family and tradition to the often - chaotic and unpredictable world of Shuri and Killmonger fanfiction.