Maybe the fanfiction could have a plot where the wizarding world is in danger again, and the granddaughter, with the help of Harry's memories or guidance (since he's reborn), has to step up and save the day. This could involve facing new dark wizards or uncovering ancient secrets.
It could be a story where Harry's granddaughter's rebirth is a result of a powerful dark magic spell gone wrong. When she is reborn, she has a unique connection to the dark side of magic. She has to fight against the influence of this dark connection while also trying to find her place in the wizarding community again. Along the way, she meets new friends and allies who help her in her journey.
One possible plotline could be Harry being easily tricked by dark wizards who take advantage of his naivete. For example, they might convince him to perform dangerous spells or go to forbidden places. Another could be that he misinterprets the intentions of his friends, causing some rifts in their relationships until he eventually learns the truth. Maybe he also gets involved with some new magical creatures that he wrongly believes are harmless because of his naivete.
One possible plotline could be Harry using his vegan lifestyle to promote animal rights in the wizarding world. He might start a club or campaign within Hogwarts to encourage others to be more conscious about their food choices.
Perhaps Harry becomes a priest to atone for the sins and destruction caused during his battles in the wizarding world. His journey could involve him trying to bring peace and spiritual guidance to a war - torn or troubled community. And along the way, he might face challenges from those who sense his 'different' past.
Perhaps Voldemort uses magic to brainwash Harry into thinking he is his pet. Harry then has to fight against this false identity while still being under Voldemort's control. The plot could involve Harry slowly regaining his true self and using his new - found knowledge of Voldemort's inner workings (from being so close to him) to defeat him in the end. It would be a journey of self - discovery and resistance.
A plotline might involve a dark magic situation where Snape has been cursed and Harry, as his donor, is the only hope to break the curse. As Harry gets involved, he uncovers secrets about Snape's past that change his perception of him. Meanwhile, Snape has to deal with his pride and accept help from someone he has long disliked, leading to a complex emotional journey for both characters.
Perhaps Snape, in a moment of weakness or out of some deep - seated sense of responsibility, decides to protect Harry in an extreme way. He treats Harry like a pet in that he provides for all of Harry's needs but also restricts his freedom. This could lead to a lot of internal conflict for Harry, who is used to being independent. Meanwhile, Snape has to deal with the other characters in the wizarding world who might not understand his motives for treating Harry this way.
Well, in fanfiction, the author has the liberty to play with the lore. There could be a scenario where a powerful dark magic spell in the past had some unforeseen consequences. This spell could have somehow intertwined the bloodlines of Voldemort and Hermione's family. Maybe a curse was placed on a family that later branched out to both Voldemort and Hermione's ancestors, creating this strange connection.
One possible plotline could be that it's the result of some dark magic gone wrong. Maybe a spell was cast on Harry by an enemy of Snape's to embarrass him, and now they have to deal with the consequences together. Another could be that it's part of a prophecy that no one expected, and they must figure out how it fits into the wizarding world's future.
One possible plotline could be Harry trying to gain Tywin's approval while also holding onto his own values. Another could be Harry using his unique skills to help Tywin in his political maneuvers.