A plotline could be that a new teacher at Hogwarts is secretly from the world of 'I am the Bone of my Sword' and is trying to find a way to combine the two magics for a greater good. But the Ministry of Magic suspects something is off and tries to stop them.
Perhaps the 'bone of my sword' power is a key to unlocking a hidden chamber in Hogwarts that is filled with ancient and powerful magic that could either save or destroy the wizarding world. A group of students discover this connection and embark on a dangerous quest.
One potential plotline could be that Harry discovers he has a bijuu sealed within him. This could explain some of his strange powers or abilities that are not accounted for in the original series. As he grows older, he has to learn to control this bijuu power, while also dealing with the usual threats in the wizarding world like Voldemort.
One plotline could be that the 'Spider King' has some sort of ancient grudge against the wizarding world in 'Harry Potter'. His minions start to infiltrate Hogwarts, and the students have to use their magic to fight back. Another could be that a prophecy in the 'Harry Potter' world mentions the 'Spider King', and Harry is tasked with finding out more about this new threat.
One possible plotline could be that Ichigo somehow gets transported to the Harry Potter world. He might use his Soul Reaper powers to fight against the dark wizards. Maybe he helps Harry and his friends in a battle at Hogwarts by using his Zanpakuto skills.
One plotline could be Moriarty infiltrating Hogwarts as a new teacher. He could secretly be plotting to steal powerful magical artifacts while also manipulating the students and staff. Harry and his friends would start to notice strange things happening around the school and suspect the new teacher. Another could be that Moriarty teams up with Voldemort, combining their evil minds to take over both the wizarding world and the Muggle world. This would put Harry in an even more difficult situation as he has to face two powerful villains at once.
One possible fanfiction idea could be a crossover where the concepts from 'I am the Bone of my Sword' are merged into the Harry Potter universe. Maybe a character from the Potter world discovers a magical sword with the essence of 'I am the Bone of my Sword' in it. This could lead to new powers and a different kind of adventure for the character.
One possible plotline could be Shirou finding himself magically transported to the Harry Potter world. He might use his skills in magic and combat from his own world to help Harry and his friends in their battles against Voldemort. For example, Shirou's ability to project weapons could be a unique advantage in the wizarding world.
Maybe the baby dragon is a rare species. This would attract the attention of magical zoologists and collectors. Harry would then have to deal with the ethical issues of keeping the dragon or giving it to those who claim to study it properly. He would also need to consider the dragon's own well - being and freedom.
One potential plotline is that a powerful artifact in the Harry Potter world has the ability to grant the wielder access to other dimensions, and it accidentally pulls Cloud into the wizarding world. Cloud, not understanding the ways of this new world at first, is seen as a threat. Harry and his friends have to decide whether to trust him or not. As they get to know Cloud, they realize his skills can be useful in their fight against the Death Eaters.
One plotline could be Sherlock growing up with some sort of magical ability that he has to hide in the Muggle world. Since Harry Potter is his father, he might inherit some latent magic. He could use this in his detective work, like being able to sense when someone is lying in a way that's more than just normal intuition, because of his magical heritage.
Well, there could be a plot where Harry, in his quest to defeat Voldemort once and for all, stumbles upon blood magic as a last resort. He might initially be hesitant but as the situation becomes more dire, he starts to explore its depths. Or perhaps, he is influenced by a new character who claims to be an expert in a different form of magic that includes blood magic, and Harry is drawn into it, believing it could give him an edge in the ongoing battle against the dark forces.