One idea could be that Harry discovers his true mother is Hela and has to deal with the new identity. He might face discrimination from some in the wizarding world who fear Hela's reputation. Another could be that he inherits some of Hela's powers, like the ability to control the dead in a more magical way than normal necromancy in the Harry Potter universe.
Perhaps Harry, as the son of Hela, is hunted by dark forces who want to use his connection to Hela for their own evil purposes. He then has to go on a journey to find out more about his mother and her powers in order to protect himself and the wizarding world. He could also meet characters from Norse mythology who are related to Hela in some way and they could either help or hinder him.
Well, a really cool plot could be that Harry's connection to Hela gives him an edge in the fight against Voldemort. He might be able to access a different kind of magic that Voldemort doesn't understand. For example, Hela's power over death could be translated into a way to counter Voldemort's Horcruxes. Maybe Harry can use his new - found powers to find and destroy the Horcruxes in a way that no one else could, all while coming to terms with his new heritage.
One idea could be that Hela somehow ends up in the wizarding world. She might be intrigued by the magic there which is different from her own powers. Maybe she tries to take over Hogwarts, thinking it's a place of great power. Another could be that Harry Potter has to team up with Hela to defeat a common enemy that threatens both the wizarding world and Asgard.
Well, perhaps the plot could involve Harry having to deal with the dual nature of his heritage. He might inherit Thor's strength and Hela's connection to the darker aspects of magic. Maybe he has to face off against enemies that are threatened by his unique lineage and the power it could bring. He could also struggle with fitting into both the wizarding world of Harry Potter and the Norse mythology - influenced world of his parents.
In this fanfiction, it could be that Hela is in need of something that only Harry can provide. Maybe a magical item from his world that has the power to heal a wound she got in a previous fight. Their meeting then becomes a journey of discovery and cooperation as Harry tries to find the item and Hela protects him during the search.
One idea could be Harry using his Poseidon - given powers to control water in the Triwizard Tournament. For example, in the second task, instead of using gillyweed, he could manipulate the water to his advantage.
One idea could be that Harry discovers his 'son of Mars' heritage gives him unique combat abilities in the wizarding world, like super - fast reflexes and enhanced dueling skills.
A possible plot could involve Harry being drawn to the Underworld to learn more about his mother. There, he meets various figures from Greek mythology who either help or hinder him. His Hogwarts friends might not understand what he's going through, leading to some tense relationships as he tries to balance his two very different worlds.
In the 'Harry Potter adopted son of vixen fanfiction', it's possible that the vixen is part of a long - forgotten magical race. Harry, as her adopted son, might be caught in the middle of a power struggle between this race and the traditional wizarding world. He could be the key to bringing peace or might have to fight to protect both his new family and his friends at Hogwarts. His vixen - influenced nature might make him more attuned to nature - based magics, which could set him apart from other wizards.
One idea could be that Harry discovers his true parentage and has to struggle with his identity. He might be torn between the side of good that he has known all his life and the dark legacy of Bellatrix. Another plot could involve him facing discrimination from both the wizarding world that hates Bellatrix and the Death Eaters who might see him as a tool or a threat. For example, he could try to use his knowledge of Bellatrix's magic, which might be more complex and dark - tinged, to fight against Voldemort in a different way than in the original story.
Maybe Harry discovers his Mikaelson heritage when strange things start to happen to him during his time at Hogwarts. His newfound powers could attract the attention of both the wizarding world and the supernatural world from Klaus' side, leading to a complex web of alliances and rivalries. He might have to learn how to balance his wizarding skills with his vampire - like abilities.
One idea could be that Harry discovers the truth about his parentage early on. This changes his relationship with Dumbledore as he realizes Dumbledore had been keeping this big secret from him. He might also struggle with his identity, feeling torn between the Gryffindor ideals he was raised with and the Slytherin traits he might inherit from Snape.