A possible plot could be that Harry has a natural affinity for runes from a young age. He starts to draw runes on his bedroom wall at the Dursleys' which have a magical effect, like keeping his room warmer or making it so that his aunt and uncle can't enter without his permission. At Hogwarts, his rune - master skills attract the attention of the professors. He could be asked to help with some important task, like deciphering a dangerous rune - based curse that is threatening the school. As he delves deeper into the world of runes, he discovers a connection between his family and an ancient rune - using wizarding clan.
Well, perhaps Harry inherits some rune - related knowledge from his parents. He unknowingly uses runes to keep himself safe from the Dursleys' worst behavior. When he finally goes to Hogwarts, he realizes that his rune knowledge is far more advanced than his peers. He might then use it to solve mysteries around the school, like decoding ancient runic inscriptions in the castle. He could also make friends with those interested in runes and together they form a sort of rune - study group that uncovers secrets about Hogwarts' past.
Yes, there are some out there. You can start by looking on fanfiction websites like Archive of Our Own or FanFiction.net. Just search for 'Harry is a Runemaster before Hogwarts' in their search bars and you'll likely find several stories to choose from.
One possibility is that they meet in Diagon Alley. Maybe Ginny is there with her family, getting her school supplies, and Harry just happens to be in the same shop. They could share a brief moment, like a shy smile or a simple hello. This encounter could be the start of a pre - Hogwarts friendship that they keep secret until they meet again at school.
One possible plot could be that they meet at a wizarding event in their early childhood. Maybe their families are both attending a magical fair, and the two boys, not yet influenced by the future rivalries at Hogwarts, strike up a friendship over their shared love for magical creatures. They might spend the day together looking at baby unicorns and discussing their favorite magical beasts.
One possible plot could be that they meet during a wizarding event in France. Fleur, being from a French wizarding family, might be at a magical fair. Harry could be there with the Dursleys on a 'family' trip (forced by the Dursleys to go to France). They accidentally cross paths and Fleur, sensing Harry's unique magical aura, strikes up a conversation. This could be the start of an interesting pre - Hogwarts friendship.
One possible plot could be that they meet in a muggle library. Hermione is there researching magic in the guise of general knowledge books, and Harry stumbles upon her while looking for a quiet place to escape from the Dursleys. They start chatting about books, and Hermione is intrigued by Harry's strange yet endearing manner. They then realize they both have a connection to the magical world.
One possible plot could be that they meet in Diagon Alley. Maybe Harry is lost while shopping for his school supplies and Daphne helps him find his way. This could start a friendship where they exchange stories about their expectations for Hogwarts. It might also be a chance for Daphne to see Harry as more than just the famous Boy - Who - Lived, and for Harry to make a friend outside of the Weasleys and Hermione.
One reason could be that he's being hidden by some powerful magic from a group that wants to use him for dark purposes. Maybe there are dark wizards who know of his future importance and want to either kill or control him, so a good wizard has made him disappear.
It depends on the specific fanfiction. There are countless fanfictions out there, and while some might make Harry a Runemaster, others may not. Some fanfictions might focus on his existing abilities from the original story, while others could take a completely different turn and give him this new role.
One possible plot is that as the heir of Hogwarts, Harry has some special powers or abilities that he gradually uncovers. He might be able to communicate with the very essence of the school, like the walls and the grounds, and they guide him in his fight against the forces of evil. For example, the castle could show him hidden passages to outwit Voldemort's minions. Also, other characters might react differently to him once they learn of his new status. Some might be jealous, while others would look to him for leadership.
One possibility is that they form an instant friendship. Maybe they discover they have a shared interest in magic even before getting their Hogwarts letters. For example, they might both have had strange experiences with objects moving on their own, and this commonality draws them together.