In this fanfiction, it could be that Harry has lost his magic temporarily. His uncle, seeing his vulnerability, takes advantage and forces Harry to submit. Harry, having no other option at the moment, obeys his uncle while secretly looking for a way to regain his magic and his freedom.
Perhaps in this fanfiction, Harry submits to his uncle as part of a deal. Maybe his uncle has some information that Harry needs desperately, like something about his parents. So, Harry endures his uncle's tyranny for the sake of that knowledge.
One possibility could be that Harry, out of a sense of duty or some form of magical coercion, decides to follow his uncle's every order in order to protect his aunt and Dudley from a new magical threat. He might suppress his own desires and instincts to keep them safe.
In this kind of fanfiction, perhaps Harry, out of fear or some form of coercion, starts to obey Uncle Vernon's every order. Maybe Vernon uses threats about expelling Harry from the house or withholding food to make him submit. This could lead to a very different dynamic in the Dursley household, with Harry being more submissive and not showing his usual defiance.
On the other hand, it could be positive in a way. Maybe through submitting, Harry learns more about his uncle's insecurities and past, which could lead to a new understanding and a form of reconciliation between them.
It could be that after a series of events that make Harry question his own judgment, he submits to Dumbledore's authority. For instance, if there are false prophecies or misinformation floating around that lead Harry astray. Dumbledore, with his greater experience and knowledge, helps Harry see the truth. So Harry decides to submit to Dumbledore in order to get back on the right track and protect Hogwarts and the wizarding world.
Some writers might create this type of fanfiction to explore a different side of Harry's character. By making him submit, they can show his vulnerability in a new way. It could also be to create a more complex relationship between Harry and his Muggle relatives, adding a new layer of drama.
One possible plot could be that Harry is sold to a dark wizard. The wizard might want to use Harry for his own dark purposes, perhaps related to the power he holds as 'The Boy Who Lived'. Harry then has to find a way to escape and seek help from his friends at Hogwarts.
One possible plot could be that Uncle Matthew discovers a secret portal between the Muggle and wizarding military bases. He gets caught up in a conflict where the two sides are unknowingly on the verge of war due to a misunderstanding. Harry and his friends then have to help Uncle Matthew resolve the situation before it's too late.
He could be a mentor. Just like Dumbledore was to Harry, Uncle John might have a wealth of knowledge about magic that he imparts to Harry. He could teach Harry some rare spells or give him advice on how to deal with the challenges in the wizarding world.
Well, one possible plot could be that Uncle Matt, being a military fan, tries to instill some military values in Harry. He might teach Harry about discipline and self - reliance. When Harry faces challenges at Hogwarts, he could use these values to his advantage. For instance, when dealing with the Dementors, he could draw on his newfound discipline to cast a Patronus more effectively.
Well, it could be a story where Lemon has some special powers that she passes on to Harry secretly. Maybe she was a hidden witch with unique magic that no one knew about, not even James Potter.
One possible plot could be that Lemon discovers a dark secret about the wizarding world that even Harry doesn't know. As they try to uncover the truth, they face opposition from some powerful wizards who want to keep the secret buried. Harry uses his skills and connections, and together with Lemon's fresh perspective and new - found magic, they fight against those who would stop them. Along the journey, their relationship as father and daughter grows stronger as they rely on each other for support and protection.