Perhaps in the 'harry is the heir of pendragon fanfiction', Harry's new status as the heir of Pendragon causes a stir in the wizarding world. Some might fear his new - found power, while others might see him as a great hope. He could be drawn into a political struggle within the magical community as a result.
One possible plot development could be that Harry has to face a lot more internal conflict. He would be associated with a house that his friends might view with suspicion. Also, he might discover new magical abilities or powers that are related to the Slytherin heritage.
Well, one possible plot development could be that Harry learns some really unique combat skills from Scathach. Maybe he becomes a much more formidable wizard in dueling. Another could be that he gains a different perspective on magic through her teachings, which helps him in his battles against Voldemort.
One possible plot development could be that Voldemort fully regains his power without Harry as an obstacle. The wizarding world would be plunged into complete darkness. His friends, like Hermione and Ron, might go into a deep state of despair and then form a resistance group. They would try to find other ways to defeat Voldemort, perhaps by seeking out more powerful magical artifacts or uniting with some previously neutral magical creatures.
One possible plot development could be how the wizarding world reacts to the loss of the so - called 'Chosen One' even as a baby. There might be widespread grief and fear among those who opposed Voldemort, as they had placed so many hopes on Harry. Another aspect could be how Voldemort's reign of terror continues without the threat of Harry Potter. He might become even more powerful and tyrannical, with no one to oppose him in the way Harry was prophesied to.
One possible plot development could be that his friends rally around him. They might search for rare potions or spells to heal him. For example, Hermione could be scouring the library for ancient healing magic while Ron stays by Harry's side, offering moral support.
One possible plot development could be that with Merlin's help, Harry discovers a new form of magic that was previously unknown. This new magic could then be used to defeat a powerful enemy.
One possible plot development could be that Harry kills Umbridge in self - defense. Maybe she attacks him first with the intent to harm or kill, and Harry has no choice but to use lethal magic in return. This would then lead to a huge uproar in the wizarding world, with some believing Harry was right and others seeing him as a murderer.
One interesting plotline could be the discovery of the connection between being the heir of Pendragon and Harry's existing powers in the wizarding world. Maybe it gives him new abilities or a different perspective on magic.
Obviously, Harry himself is the central character. Then, there could be characters like Dumbledore who might play a role in guiding Harry about his new heritage. Hermione would also likely be involved, using her knowledge to help Harry understand the Pendragon history.
There could be other characters from the original Harry Potter series who play important roles. For example, Hermione might be there to help Harry research and understand his Pendragon heritage. Ron could also be by his side, providing support and comic relief in the face of all the new and strange things that come with this discovery.