One possible storyline could be that Harry has to hide his new identity as the 10 - Tailed Demon from the wizarding world at first. He might be afraid of how people will react. As he tries to keep it a secret, he has to deal with the internal struggle of controlling this new power.
In fanfiction, when Harry is portrayed as the 10 - Tailed Demon, it often brings a whole new level of power and mystery to the character. It might be a concept where he has to control this immense power, perhaps in a world different from the original Harry Potter universe. This could lead to new storylines and character developments.
One possible storyline could be Harry making friends with students from different houses at Hogwarts. For example, he befriends a shy Ravenclaw who helps him with his studies in a unique way. Another could be Harry befriending magical creatures, like a friendly centaur who gives him advice on dealing with the Forbidden Forest.
Maybe there could be a story where they grow up together, but due to their different abilities, they face discrimination in their world. They then have to fight against the prejudice while also trying to figure out their family secrets. Harry's Hogwarts experiences and Uryu's experiences in the Soul Society could be compared and contrasted as they struggle to find their place in the world together.
A possible storyline could be that a lost grimoire is found which contains spells using Belladonna. The finder, perhaps a young witch or wizard, has to figure out how to use it without getting poisoned by the Belladonna - related magic. This could lead to a series of trials and learning experiences as they navigate the dangerous and unknown magic.
Well, a storyline could involve Harry's connection to other phoenixes. Since he's part phoenix, he might be able to communicate with them on a deeper level. This could lead to him getting help from the phoenixes in the fight against evil. Or perhaps he discovers that his phoenix side gives him a special immunity to certain dark magic, and he has to figure out how to use this to protect his friends and the wizarding world.
Well, a storyline could involve Dumbledore kissing Harry as a way to seal a magical pact. This pact could be related to protecting Hogwarts or the wizarding world from a great threat. It might also be a situation where Dumbledore's actions are misinterpreted by others in the wizarding community, leading to a lot of drama and conflict. And in some fanfictions, it could be a moment of time - bending magic where Dumbledore from the past or future comes to Harry and the kiss has some profound significance for the timeline.
One possible storyline is that the marriage contract is part of a dark plot. Some evil force in the wizarding world might be using it to manipulate Harry and Narcissa. They then have to work together to figure out who is behind it and how to break the contract if they don't want to be married. Another idea could be that the contract was made long ago to protect something or someone. Harry and Narcissa have to uncover the secrets behind it.
One possible storyline could be that Harry Peverell is on a quest to uncover a long - lost secret of Westeros. This could lead him to interact with various major and minor characters from the Game of Thrones world as he follows the clues. Another storyline might be that he is involved in a power struggle within a particular region, vying for control against other ambitious lords or ladies.
Maybe some of the old grudges between wizarding families that were thought to be resolved start to flare up again. This could lead to a lot of political intrigue within the wizarding community. And the children of the main characters could get caught up in this web of family feuds, having to decide whether to follow their family's old ways or try to make peace.
One possible storyline could be that Harry is cursed by a dark wizard. The curse has the unexpected side - effect of making him pregnant. He then has to search for a way to break the curse while dealing with the physical and emotional turmoil of pregnancy. Another could be that it's a result of some experimental magic gone wrong. He might have been trying to help someone with a fertility spell and it backfired on him.