In this fanfic, perhaps the demon's soul is somehow connected to Voldemort's resurrection. Harry and his friends might go on a quest to find the origin of this demon's soul connection. They could encounter new magical creatures and spells along the way that are associated with the demon's soul's power. For example, they might come across a forest where the trees are possessed by the dark energy of the demon's soul, and they have to find a way to pass through without being affected.
Well, it could be about Harry Potter having to face a new kind of dark magic related to the demon's soul. Maybe he discovers a hidden artifact that is infused with the demon's soul and has to figure out how to destroy it without getting corrupted himself.
Maybe the demon's soul itself could be the main antagonist in a way. It has its own will and desires, which are mainly to spread chaos and destruction. It could possess other characters in the story and make them act against Harry. For instance, it might possess a Hogwarts professor who then tries to undermine Harry's efforts to stop it. The demon's soul's ability to manipulate and corrupt would make it a very dangerous and menacing antagonist.
Well, perhaps Harry could be transported to Soul Society. He might discover new magical abilities related to souls there. Maybe he'd interact with the Soul Reapers, learn their ways of handling souls and spirit energy, and use his own magic in unique ways within the context of Soul Society.
The plot could be that Harry, raised by demons, has unique powers that other wizards don't. For example, he might be able to communicate with dark creatures more easily. The demons could be using Harry as a tool to infiltrate the wizarding world. When he gets to Hogwarts, he starts to question his upbringing as he sees the kindness and different ways of magic there. He has to decide whether to stay true to his demon - raised self or embrace a new way of life.
One possibility is that Harry Potter, in this fanfiction, might be exposed to a whole new set of dark magic and powers that demons possess. The demons could see his potential and decide to raise him in a way that is completely different from the wizarding world he knew. Maybe they would teach him to use his magic more aggressively or in ways that are considered unethical in the normal wizarding community.
Perhaps the story could show Harry being isolated from the wizarding world he was meant to be a part of. Since demons are raising him, they might keep him away from Hogwarts and the positive influences there. He could develop powers that are a mix of wizardry and demonic abilities, which would make him a very different kind of character in the fanfiction universe. He might also have a different view on good and evil, as demons' moral compass is not the same as that of humans or wizards.
Well, it could be a really wild plot. Maybe Harry discovers he has the ability to use his magic to make demons sing, and he uses this as a way to defeat Voldemort. For example, the demons' singing could have some kind of magical effect that paralyzes the dark forces.
In the 'Harry Potter Saved by Demons' fanfiction, perhaps the demons are not as evil as they seem in the traditional sense. They might be outcasts from their own demon realm. When they come across Harry, they recognize his power and the danger he's in. They decide to save him because they believe that by doing so, they can change the fate of both the wizarding world and their own world. So they use their unique demon abilities to keep Harry safe from harm.
One possible plot could be that Harry discovers he has the ability of a Soul Reaper. He then has to balance his life at Hogwarts with his new - found duties as a Soul Reaper. For example, he might have to deal with Hollows (evil spirits in Soul Reaper lore) that are lurking around the Forbidden Forest.
Hermione could be one. Given her open - mindedness and thirst for knowledge, she might be intrigued by the Demons Child and see its potential for good rather than just being scared of it.
Well, perhaps Harry could be a weapon that has the power of his magic from the Potter world. He might be used by a Soul Eater character to fight against evil souls. Maybe his wand could transform into a more weapon - like form in the Soul Eater world.