A young thief could be the main character. They steal the dragon's skin thinking it's just a valuable item but then find out about its strange properties.
It could be a knight who is on a quest to slay a dragon. Instead of killing the dragon, they end up with its skin and decides to wear it. This could lead to a moral dilemma within the character as they start to feel a connection with the dragon they were supposed to kill. The knight would then have to navigate their new identity while still being part of a society that fears and hates dragons.
Maybe an outcast wizard. They are shunned by their wizarding community for their unorthodox ways. They discover the dragon's skin and wear it as a way to gain power and respect. As they wear the skin, they learn to control new magic that is associated with the dragon, and the story could be about how they use this new - found power to either seek revenge or to prove themselves to their former community.
Another concept could be that the dragon's skin is a magical heirloom passed down through generations. The main character has to wear it to fulfill a prophecy. While wearing it, they experience visions of the dragon's past and must use this knowledge to save their world from an impending doom.
It could be the dragon itself. The story could be told from the dragon's perspective, showing its thoughts and feelings as it uses its roar for various purposes.
A young princess could be the main character. She is often seen as a symbol of purity and royalty. The kingdom might be in a dire situation due to the dragon's attacks, so they offer her as a sacrifice. She then has to use her wits and any hidden powers she may have to deal with the dragon, perhaps even trying to change the dragon's nature.
Perhaps a young and inexperienced adventurer who discovers their hidden power while on the quest to slay the dark dragon. They grow throughout the story, learning new skills and becoming a true hero.
It could be a new character created specifically for the fanfiction. Maybe a young ninja who discovers the neglected dragon and forms a bond with it.
An akumatized villain could be the main character in a different kind of fanfiction. The villain was once a normal person but due to some heartbreak or injustice, they are akumatized into a dragon - like form. The story could then be about their journey of redemption or how Ladybug and Chat Noir try to bring them back to their normal self.
A young orphan who has been training to be an ice dragon slayer since a young age. They have a strong will to prove themselves in a world that has always looked down on them because of their lack of family and resources.
It could be a fearless knight. He has been on many quests before but when he hears the lightning dragon roar, he realizes it's a call to a greater adventure. He has to use his combat skills and courage to face whatever the roar signifies, whether it's a battle against a powerful enemy or a journey to find a lost treasure.
Sasuke could also be a great main character in this fanfiction. Given his drive for power, he might be the one to seek out the dragon armor and use it to further his own goals. He could have an interesting journey of learning to control the power of the armor while also dealing with his inner demons.
It could be an existing character like Naruto who, through some strange turn of events, gains the Wood Dragon Slayer power. This would completely change his fighting style and how he approaches challenges. He could use the power in creative ways, like combining it with his Rasengan to create a new, more powerful attack.