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 a character getting hit by a powerful dark spell during a battle, which causes brain damage. Then the story could revolve around their struggle to regain their magical abilities and memories. For example, if Harry were to be the one with brain damage, he might have to relearn spells and how to interact with his friends in Hogwarts.
One possible storyline is that the Potter Manor is under attack by a new dark force. Harry and Ginny have to defend it using their skills and the help of their friends. Another could be that they are renovating the manor and discover some long - lost family secrets during the process.
One possible storyline is that the marriage contract is discovered during a time of great unrest in the wizarding world. Harry and Narcissa are forced to work together to protect their interests. Another could be that the contract has some sort of magical binding that forces them to get closer. This leads to an unexpected emotional connection between them. For example, they might start to care for each other while trying to figure out how to deal with the contract.
One possible storyline could be Harry growing up in the Naruto world with Jiraiya as his father. He would learn ninja techniques instead of magic at first. But then, as his wizarding powers start to show, he has to balance both worlds. Another could be that Jiraiya takes Harry on adventures in both the ninja world and the wizarding world, introducing him to different characters from both universes. Maybe Harry uses his magic to help in ninja battles in a unique way.
A possible storyline is that Ruby Rose, with her combat skills, trains the students at Hogwarts in self - defense against the dark arts. Harry Potter might be initially skeptical but then realizes the value of her unorthodox methods.
One storyline could be that Harry, after the events in the wizarding world, decides to take a break and travels to Gotham. There he meets Bruce, and they end up teaming up to take on a new threat that combines magic and Gotham's usual criminal element. Maybe a villain who has somehow gotten hold of a powerful magical artifact and is using it to wreak havoc in the city.
One possible storyline could be that the hobgoblin is a magical creature that has been trapped in Hogwarts for centuries and Harry discovers it. The hobgoblin then teams up with Harry to uncover the secrets of Hogwarts that are related to a new dark threat. Another could be that the hobgoblin is a messenger from an unknown magical realm and it chooses Harry to be the one to communicate with its realm.
Well, it could be a story where Harry is tricked into believing that Muggles are responsible for some great harm to his loved ones in the wizarding world. So, in his rage and misdirected sense of justice, he starts targeting Muggles. But this is a very un - Harry - like behavior as the real Harry is all about protecting the innocent, whether they are wizards or Muggles.
One possible storyline could be Harry's struggle for freedom. He might try to find ways to escape the slavery system, perhaps by befriending some sympathetic characters within the slave - holding society. Another could be his discovery of hidden powers or skills that give him an edge in his fight for liberation.