His magic could develop in a more secluded and family - centered way. His grandparents might have their own unique magical knowledge, passed down through generations. They could start by teaching Harry basic spells in the privacy of their home, away from the prying eyes of the wizarding world. For example, they might show him how to use magic to tend to their garden, making the plants grow faster and healthier.
In this fanfiction, his grandparents might be described as having a deep connection to the magical land they live in. They could be the keepers of ancient family secrets. Their physical features might be aged but still show signs of the great beauty and strength they had in their youth. And they may be very loving towards Harry, making up for the lost time they could have had with him.
Perhaps his grandparents were great adventurers in their time. They could have traveled to far - off magical lands and encountered strange and wonderful things. Their experiences could be passed on to Harry, inspiring him to explore more of the wizarding world and its secrets. They might also have been involved in some great battles in the past, and their war stories could give Harry valuable lessons for his own fight against Voldemort.
They could be very traditional and strict pure - blood wizards. Maybe they were part of some ancient magical order and had high expectations for the Potter family. They might be disappointed in how James and Lily Potter deviated from some of the old ways, but be very proud of Harry when they get to know him.
In such a fanfiction, perhaps the story could show Harry growing up with a different kind of family dynamic. His grandparents might instill in him values that are different from what he would have learned at the Dursleys'. For example, they could be more open about his magical heritage from the start, which would lead to him being more confident in his abilities as he grows. Maybe they would also have their own set of magical friends and connections that would introduce Harry to a different side of the wizarding world earlier.
One possibility is that Harry's grandparents help him uncover his family's true history. They could show him old family portraits and explain the relationships and events that led to the present situation. His grandparents may also have a different perspective on the fight against the dark forces. They could advise Harry on how to use his powers more effectively and how to build alliances. And they might even be the ones to finally reveal the full story behind the prophecy related to him.
Maybe Harry will have an emotional reunion. He could finally learn about his family history that his parents might not have had the chance to tell him. His grandparents might share stories about his parents' childhood, which would give Harry a deeper understanding of his family roots.
One possible fanfiction could be that Harry is sent back in time by a powerful magical spell gone wrong. He lands in a time when his grandparents are young and full of life. He has to figure out how to get back while also trying not to disrupt the timeline too much. Maybe he helps his grandparents in some small way that has a big impact on his own future.
Perhaps in the fanfiction, Harry discovers that his grandparents had a hidden magical legacy. They had been working on a powerful charm to protect the Potter family long before Harry was born. Harry finds clues about this charm and with the help of his friends, he tries to complete it, believing it could be the key to finally defeating Voldemort.
He might be more old - fashioned in his ways. His grandparents' values would likely have a big influence on him, so he could be more reserved and traditional compared to the Harry we know from the original series.