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.
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.
I'm not entirely sure if there is a specific 'Harry Potter summons the devil' fanfic. Fanfiction is a huge realm with all kinds of ideas. But in the official Harry Potter universe, magic is more about good - evil magic like summoning the devil is not in line with the main story. It could be a very niche and probably not very popular idea among the more traditional Harry Potter fans.
The servant could do household chores. Just like how house - elves in the Harry Potter world usually take care of cleaning, cooking, and keeping the place tidy. For example, if Harry is living in Grimmauld Place, the servant could make sure the old and gloomy house is clean and habitable.
Many fanfics depict the order summons as a form of enchanted parchment. The sender writes the details of the summons on the parchment. Once it's complete, the parchment magically replicates and finds its way to each member of the order. The parchment might have a special seal or symbol that only the members recognize, ensuring secrecy and authenticity.
It would be very different from the normal Harry Potter stories. It might involve dark magic and a deviation from the moral code of the wizarding world. Maybe Harry would be in a desperate situation and make a really bad choice to summon the devil.
Well, one possible plot could be that the servant Naruto summons is from a future time. This servant has knowledge of events that are yet to happen in the Naruto world. Naruto then has to use this knowledge wisely while also keeping the servant's origin a secret from others who might misuse it.
Yes, it's possible. In many fanfictions, the main character has to find a way to control whatever they summon. Harry, being a powerful wizard in the original series, might use his magic skills and knowledge to control the demon. He could use spells or magical objects to keep the demon in check.
In some fanfics, an order summons might be a magical charm that appears as a constellation in the sky, visible only to those who are part of the 'Order'. For instance, if the Order is reforming to fight a resurrected Voldemort - related threat, the summons could call wizards from all over the wizarding world to a hidden location like the Room of Requirement.