Maybe an old sage - someone who has seen the world decline over time. They have knowledge and wisdom, and the single flame might be something they have been waiting for. They could use their experience to guide others in a world that is falling apart.
A young and idealistic person might be the main character. They see the single flame as a sign that all is not lost and decide to fight for the world's survival. They could inspire others around them to also take action.
It could be a lone wanderer. This type of character often has a mysterious past and is searching for something in the dying world. They might be drawn to the single flame for reasons they don't fully understand at first.
It could be about a character who tries to keep the last bit of hope alive in the dying world. Maybe they are on a journey to find a way to revive the world.
Sasuke could be a great main character in such a fanfiction. He has a deep connection with Naruto. If Naruto's dying will flame is involved, Sasuke might be on a journey to understand what Naruto left behind and how to carry on his legacy. He could be conflicted between his own past and the new responsibility that comes with the dying will flame.
The main character could also be a new character created specifically for the fanfiction. This new character might be someone who is deeply affected by the will of the single man, and the story could be told from their perspective as they navigate the consequences of that will.
Natsu could be a great main character. Since he already has a strong connection to fire, his encounter with the Flame God could lead to him unlocking new levels of power. He could learn unique fire - based spells and techniques from the Flame God, which would be exciting to read about.
It could be a new character created specifically for the fanfiction. Maybe a young girl who has always felt different because of the guiding flame she possesses.
Maybe a male wizard who has fallen in love with a witch from a more well - off family. His family can only offer a single galleon as dowry, and he has to prove himself worthy in other ways, like through his magical feats or his kind heart.
Ruby could be a great main character for a 'rwby silver flame fanfic'. Given her natural leadership and combat skills, she could be on a quest to understand and control the Silver Flame, perhaps believing it could be a new weapon against Salem.
A powerful dark dragon could be the main antagonist. This dragon might be jealous of the little flame dragon's unique abilities or position within the dragon community. It could constantly try to undermine the little flame dragon and cause trouble for it.
It could be a powerful alien warlord who wants to use the dying reader's unique energy for his own evil purposes. Since the reader is in a vulnerable state, this antagonist sees an opportunity to gain power.
A female cultivator could be the main character. She might be on a quest for revenge in her own world but gets sucked into the DxD world instead. In the DxD world, she has to start from scratch in a sense. She uses her wits and cultivation skills to survive and eventually rise to power. Her gender could also play an interesting role as she might face different challenges compared to a male character in a world that also has its own ideas about gender roles and power dynamics.