One idea could be exploring Annie Cresta's pre - Games relationships in more depth. Maybe she had a secret friendship or alliance that affected her during the 70th Hunger Games.
Perhaps a plot where Annie has to use her unique skills, like her swimming ability, in unexpected ways during the Games. For example, she could use flooded areas of the arena to her advantage. Another aspect could be delving into her mental state during the Games. Since she is known to be a bit unstable, showing how she copes with the stress and brutality of the 70th Hunger Games could be really interesting.
One idea could be that Annie forms an unexpected alliance with a Career tribute who later betrays her. This would add drama as she has to fight back and use her wits.
Finnick could be an obvious ally. Since they have a relationship, he would surely want to protect her and help her survive the 70th Hunger Games.
Well, Annie Cresta from The Hunger Games. She participated as a tribute from District 4. During the games, she must have faced many challenges and horrors. Her win didn't come without a cost as she ended up with serious mental trauma. In the world of The Hunger Games, survival doesn't always mean a happy ending. Annie's story shows that even after getting out of the arena alive, the nightmares and the memories can still be a prison. And with Finnick by her side, she was still struggling to deal with her past in the games.
One idea could be to focus on a new type of arena. For example, an arena that is constantly changing, like it shifts from a desert to a frozen tundra. Another could be to explore the backstories of the tributes more deeply. Maybe one tribute has a secret connection to the Capitol that they are trying to hide. A third idea is to have a group of tributes form an alliance not for survival in the games, but to send a message to the Capitol about the cruelty of the Hunger Games.
One common theme is trauma. Given what Annie has been through in the Hunger Games, many fanfics explore how she copes with the mental and emotional scars. Another theme is love, especially her relationship with Finnick.
A third common theme is her connection to the water. Since she's from a district known for fishing, many fanfictions use her love for the water as a symbol of her strength and also as a way to heal from her traumas. In some fics, she has a spiritual connection to the water that helps her move forward in life.
Maybe a tribute from a different district who starts off as an enemy but then realizes they have more in common with Annie than they thought. Their relationship could develop slowly during the games.
One idea could be to focus on a new kind of arena. Maybe an arena that changes based on the tributes' fears. For example, if a tribute is afraid of water, parts of the arena would flood when they're nearby. Another idea is to create a group of tributes who form an alliance not for survival, but to rebel against the Capitol from within the Games.
One key event was her winning of the Hunger Games which was likely filled with terrifying moments. Another is her relationship with Finnick Odair which became important in the overall story. Also, her mental breakdown due to the trauma of the games is a significant event as it shows the dark side of the games' aftermath.
One idea could be a tribute who has a unique survival skill like being able to communicate with animals in the arena. They could use this to gather information about hidden resources or approaching threats.