In a 'Harry and Ron not friends fanfiction', perhaps there's a misunderstanding about a family heirloom. Ron thinks Harry has taken something that belonged to the Weasleys. Harry denies it, but Ron doesn't believe him. This leads to a breakdown in their friendship. As a result, they form different groups within Hogwarts, and there's constant tension between the two groups.
One possible plot could be that they have a major disagreement over a Quidditch match. Maybe Ron blames Harry for losing the match because Harry made a risky move that didn't pay off. This causes a rift between them, and they start to see each other as rivals rather than friends. They compete in everything from academics to getting the attention of a certain teacher.
One possible reason could be a divergence in their goals. Maybe in the fanfiction, Harry has a different approach to fighting Voldemort and Ron doesn't agree with it, leading to a rift. For example, Harry might want to take a more aggressive and risky approach while Ron prefers a more cautious one. This difference in ideology can drive them apart.
It could be Draco Malfoy. Since Harry and Ron are not friends, Draco could take advantage of their weakened state. He might try to turn them against each other even more, perhaps by spreading false information about one to the other. He could also try to isolate Harry from the Gryffindor group since Ron is no longer on his side, making Harry an easier target for his bullying.
It could be that Ron and Hermione abandon Harry due to a prophecy that they misinterpret. They believe that by being with Harry, they will bring doom to the wizarding world. So they go into hiding. Harry, on the other hand, is determined to change the course of the prophecy. He embarks on a journey to find the truth behind it, all while feeling the pain of his friends' desertion. He has to fight against dark forces that are taking advantage of the situation.
In such a fanfiction, it might be that Harry and Ron are influenced by a powerful dark spell. This spell makes them see Hermione as a threat, so they abandon her. Hermione then has to find a way to break the spell's influence on them while also dealing with the loneliness and danger she's now in. She could seek help from other Hogwarts students or even some friendly magical creatures.
In this fanfiction, it could be that Creevey is being bullied by some Slytherin students. Harry, being his friend, steps in to protect him. Harry then decides to teach Creevey some basic self - defense spells. As they practice together, they not only grow closer as friends but also Creevey gains more confidence. This newfound confidence leads Creevey to stand up for other students who are being bullied, and he and Harry become a symbol of friendship and standing up for what's right at Hogwarts.
One possible plot could be that they team up for a magical tournament that's different from the Triwizard Tournament. They discover they both have a passion for a rare branch of magic and decide to research it together, facing various challenges along the way.
Well, a plot could revolve around Lavender helping Harry deal with his fame. Since she's more in tune with the social side of Hogwarts, she could teach Harry how to handle the attention he gets. In return, Harry could help Lavender with her studies, especially in Defense Against the Dark Arts. This exchange would form the basis of their friendship and be the main plot thread throughout the fanfiction.
Well, it could be about Harry and Barty getting to know each other through a shared interest in magical creatures. Maybe they meet in the Forbidden Forest while Harry is on detention and Barty is secretly researching a rare creature there.
One possible plot could be that Harry and Neville discover a hidden chamber in Hogwarts that is full of ancient magical plants. Neville, with his love for Herbology, is excited and they both explore it. Along the way, they face some magical creatures protecting the plants and they have to use their combined skills of magic and Neville's knowledge of plants to get through. It could strengthen their friendship as they rely on each other.
One possible reason could be a misunderstanding. Maybe a miscommunication led to a rift between them. For example, if Harry overheard Ron saying something that was taken out of context, it could start the breakdown of their friendship.