It could be a house - elf. House - elves are known for their loyalty and their ability to do various tasks. They could be very useful to Harry, like helping him keep his dormitory clean or even spying on the Death Eaters.
In Harry Potter servant fanfic, the idea of a servant having a special power or gift that aids the main characters is quite common. This power could be something like the ability to communicate with magical creatures in a deeper way, which then helps Harry and his friends in their adventures. It adds a new layer of mystery and assistance to the story.
Well, in such a fanfic, Harry might summon a servant with unique powers. Maybe the servant could help him in his battles against Voldemort. For example, the servant could have the ability to detect dark magic from afar, allowing Harry to be more prepared for attacks.
Another possibility is Winky. She is also a house - elf. Winky was a bit of a tragic character in the original books. In the fanfiction, if Harry were to summon a servant, her meek and somewhat lost nature might make for an interesting addition to Harry's side, and she could be summoned to help Harry with various tasks.
Sometimes, minor characters from the books like the caretaker Filch are also given a new perspective as a servant - like figure. Fanfic writers might explore his past or give him a more important role in serving the Hogwarts community in ways that were not fully explored in the original books.
Harry Potter himself could be the Servant of God. Given his central role in the original series, it would make sense for him to take on this new identity in the fanfiction. He has always been a figure of good, and this could be an extension of his character arc, where he now serves a higher power in a more direct way.
One possibility could be a story where a character from Harry Potter becomes a servant in the Fate universe. For example, Harry himself could be summoned as a servant. His magic from the Potter world might interact in interesting ways with the rules of the Fate system. He could use spells like Expelliarmus against other servants, and his ability to resist the Dark Arts might give him an edge in battles.
Another concept is that a fem servant from a different magical realm ends up in Hogwarts. She befriends Harry Potter and uses her unique skills as a servant, like being extremely organized and observant, to help Harry and his friends solve mysteries and overcome challenges in the castle.
One interesting 'Harry Potter servant fanfiction' could be those where house - elves are given more in - depth storylines. For example, a fanfiction might explore Dobby's life before he met Harry in greater detail, including his relationships with other house - elves. Another could be about a wizard or witch who, instead of having a traditional familiar, has a human servant with magical abilities. There are also fanfictions that might focus on a servant character who discovers a long - lost magic and uses it to change their status within the wizarding world.