Well, there's the boy from District 9 that we barely see in the games. He could be a great character to focus on. Maybe he has some unique skills or knowledge that could change the course of the games if he was given more of a chance. Also, the Capitol's stylists for the less - popular districts are often overlooked. They could be really interesting, like they could be secretly helping the tributes in ways other than just making them look good. And the Peacekeepers from the smaller districts could also be a focus. They might have their own internal struggles about following the Capitol's orders.
One idea could be a story about a character who was thought to be dead in the original Hunger Games but actually survived and is now plotting revenge against the Capitol. Another could be a fanfic focused on the love story between two tributes from different districts that was never explored in the original books. Maybe a story about a group of rebels who use the Hunger Games arena as a base for their operations against the Capitol.
Rue is often seen as a secondary character, but she could be a great focus in fanfiction. There's so much more to her than just being Katniss's ally. Her skills in the trees and her knowledge of plants could be explored further. Also, Foxface is really underrated. She was so smart in the Games, and a fanfiction could delve into her thought process, like how she planned her moves and how she managed to survive for so long without getting into direct confrontations.
The house staff could be underrated characters. They've been around the Hawthorne family for a long time and surely know a lot of secrets. Focusing on them could add a whole new layer of intrigue to the story.
Jenna is obviously a key character. You can explore her character further, like what if she had different reactions to becoming 30 in the fanfiction? Maybe she's more scared or more excited than in the movie.
The Wasp. She is a powerful and intelligent character. A fanfiction could center around her leadership skills within the Avengers. Maybe she has to lead the team in a situation where all the big - name heroes are incapacitated. It would show her strategic thinking and her ability to inspire others.
The stable hands who take care of the dragons often get overlooked. They have a unique perspective as they interact closely with the dragons on a daily basis. Fanfiction could explore their lives, their dreams, and how they view the dragon riders.
The White Rabbit is often just seen as the one who leads Alice into Wonderland, but he could be so much more in fanfiction. He could be a time - traveler, for example, and his hurry is because he's always on a tight schedule to different eras. The Tweedle brothers are also underrated. They could be the key to unlocking some ancient secrets of Wonderland. In a fanfiction, they could lead Alice on an adventure full of riddles and puzzles that reveal the true nature of Wonderland. And the Caterpillar is quite an interesting character to focus on. It could be a wise sage who holds the knowledge of the entire Wonderland universe.
Shino Aburame is quite underrated. In a fanfiction, he could be shown as a key figure during the Revolution. His unique insect - based jutsu could be developed further, and his calm and intelligent nature could be used to his advantage in the political and social upheaval of the time.
Hot Pie. He may seem like a minor character, but he has a lot of potential. A fanfiction could explore his life after leaving Arya. Maybe he becomes a famous baker in a large city, and through his bakery, he gets involved in the political intrigues of the city as people from all classes come to his establishment.
Hot Pie is an underrated character. He could be the focus in a fanfiction where his baking skills become more than just a side note. Maybe he bakes special treats that have magical or medicinal properties and gets caught up in the big political and power struggles because of it.