He could be a wizard who made a deal with a powerful magical entity. In exchange for great power, he lost his face. Now, he appears in the story of Harry Potter, and his presence might be a sign of a greater, more complex plot involving power struggles within the wizarding world that Harry will eventually get caught up in.
He could be an ancient wizard who was cursed and lost his face. In the fanfiction, this wizard might be seeking a way to reverse the curse and his journey intersects with Harry Potter's adventures.
There could be a fanfiction where the Faceless Man is a time - traveler. He travels through different eras in the Harry Potter universe, influencing events in ways that no one realizes. For example, he could be the reason some spells were created or some dark wizards were defeated in the past, all while remaining faceless and mysterious.
Well, perhaps the faceless man is a time - traveler from a far - off future of the Harry Potter universe. He comes back to Harry's time with knowledge of a great disaster that's about to befall the wizarding world. He tries to guide Harry in a way that will change the future, but his faceless nature makes him seem very mysterious and untrustworthy at first. Harry has to decide whether to trust this strange being or not, which could lead to a really interesting story.
One possibility is that Jon Snow uses his new Faceless Man skills to infiltrate the Boltons' camp undetected. He could change his face to look like one of their soldiers and gather crucial intelligence for the Starks.
One idea could be Arya using her Faceless Man skills to avenge the wrongs done to her family. She could infiltrate the enemies' strongholds unnoticed and take them out one by one.
One great fanfiction could be 'Jon Snow's New Path'. In this story, Jon Snow discovers his connection to the Faceless Men in a very unexpected way. It delves deep into his struggle with his new identity and the powers that come with it. The author does a wonderful job of blending the mystery of the Faceless Men with Jon Snow's own character arc from the original series.
He could be recruited by the Faceless Men. Maybe they saw potential in him, perhaps his skills or his thirst for a new identity led them to approach him and offer him the chance to become one of them.
Arya might use her Faceless Man abilities to protect the common folk. She could disguise herself as different people and gather information about threats to the villages. Then she would act to stop those threats, like bandits or corrupt lords preying on the weak.
Since I'm not certain which 'got faceless man story' you mean, it's hard to pinpoint its origin. But if we think about faceless figures in general, in some ancient mythologies, faceless entities were sometimes used to represent the primordial chaos or the formless void before creation. Maybe this 'got faceless man story' has some roots in such ancient concepts, though it could also be a modern creation inspired by those old ideas.