I'm not sure specifically what this particular fanfiction is about as there could be countless interpretations. It might focus on the events, characters, or new storylines within the Hunger Games universe.
Survival is a very common theme. Just like in the original Hunger Games and the Purge concept, characters in the fanfiction have to fight to stay alive. They face various threats and have to use their wits and skills.
There could be a mentor character who was a previous Hunger Games winner and is now guiding the new tributes. This character might have their own secrets and motives, and their backstory and how they interact with the tributes can make them a popular and complex character in the fanfiction.
It could be about a new tribute who has a unique skill like being able to communicate with animals. They use this skill to survive in the arena, forging alliances with other tributes who are also outsiders in their own districts.
One idea could be to focus on a new tribute from an overlooked district. This tribute could have a unique skill, like being an expert in camouflage. They could use this skill to their advantage in the arena, hiding from other tributes and surprising them when they least expect it.
Another good one is 'Purge and the Games'. In this fanfiction, the concept of the annual purge is somehow incorporated into the Hunger Games itself. It's really creative as it combines the two concepts in a unique way, making for a very engaging story.
A plot could involve a love story within the Hunger Games. Maybe a tribute falls in love with someone from another district during the training period. This love gives them extra motivation to survive and protect the other person. They could try to find ways to both survive the games, which is against the rules, adding a lot of drama.
Perhaps an older brother who volunteers to take his younger sister's place in the 50th Hunger Games. He has a strong sense of family loyalty and his journey in the Games could be about protecting the other tributes who remind him of his sister.
One idea could be to focus on a new type of arena. For example, an arena that is constantly changing between different biomes like a desert one moment and a frozen tundra the next. This would add a whole new level of challenge for the tributes.