It could be a summon. Just like how Naruto has toads and Sasuke has snakes, a character in a fanfic could have a salamander as a summon. It could have unique abilities like being able to camouflage in water (since many salamanders are associated with water) and use that for stealth in battles.
Perhaps the salamander could be a guardian of a hidden place in the Naruto world. This place could be full of secrets, like a new type of jutsu scrolls or a special training ground. The salamander would be the first line of defense for this place. Any character who wants to access this place would have to either befriend the salamander or defeat it in a battle. And the story could be about a young ninja's journey to this hidden place and their encounter with the salamander.
He might be a disruptor. His overpowering strength and different fighting style could shake up the existing power structures in the Naruto universe. He could also be an explorer, coming from his own universe and being curious about the Naruto world, which could lead to many adventures and interactions with different characters.
Since it's a fanfic, the plot could be all over the place. It could be that Naruto gets a salamander summon instead of the toads. This would change a lot of his battle strategies and how he approaches different situations in the Naruto universe. The story might also explore the origin of the salamander in the Naruto world and how it relates to Naruto's own powers or his clan.
It could be a key plot device. For instance, if the beam katana is the only weapon that can defeat a powerful new villain who has a chakra - absorbing shield. The hero must then search for the knowledge to unlock the full potential of the beam katana to save the village.
Perhaps she is a messenger from a different realm that holds secrets related to the Naruto universe's origin. The Silent Hill nurse might hold some knowledge that is crucial for the main characters. However, she only reveals it in a very cryptic and disturbing way. So the ninja have to figure out how to communicate with her and get the information without losing their minds in the process.
The Happy Mask Salesman might be a mysterious figure who shows up in key moments. He could be a sort of catalyst for certain events. Maybe he gives a mask to a young Naruto that unlocks a hidden power within him, but at the same time, comes with a dangerous price or curse that Naruto has to figure out how to deal with. This would add a whole new layer of complexity to Naruto's journey.
Hyourinmaru could be a key to unlocking a hidden power within a character. For instance, a young ninja discovers an old scroll that mentions Hyourinmaru. As they study it, they find that it holds the secret to a new form of chakra control related to ice. This then gives them an edge in combat and in their journey to become a stronger ninja.
Rena may be a key figure in a new adventure within the Naruto fanfic. Maybe she has a special mission that involves the main characters, like finding a hidden treasure that has the power to change the balance of power in the ninja world. So she's like a catalyst for a whole new set of events.
Blake could be a mentor figure. In the fanfic, they might have extensive knowledge of a rare or forgotten ninja art and teach it to the younger generation of ninjas. For instance, they could teach about a special type of taijutsu that was lost in history. They would then guide the characters in using this new skill in their quests.
Power growth is another common theme. The salamander summoners typically start at a relatively low level of power and gradually become stronger. They train, face challenges, and learn new techniques related to their salamander summoning. This could involve learning new jutsu that the salamanders can perform or improving the connection with their summoned creatures.
Female Harry could become an influential outsider. Since she has different powers and a different background, she might be able to influence the politics in a way that no one in the Naruto world has thought of. Maybe she could form alliances with certain clans based on mutual interests. For instance, if a clan is interested in learning about her magic, she could offer knowledge in exchange for support in the political arena. She would have to be careful though, as there are always those who would oppose any change or outside influence in the clan politics.