Another possibility is that in the fanfic's unique plot, there could be some sort of magical influence or dark magic at play. Perhaps a spell was cast on Ron that made him act out of character and punch Harry. It could also be part of a complex plot where Ron is being controlled by an outside force to create drama between him and Harry in the context of the Drarry relationship.
It could also lead to a divide within their group of friends. Hermione, for instance, might be caught in the middle, not knowing who to side with. This could create a lot of tension and conflict among the characters, adding more drama to the fanfic. If the punch was public, it could also damage Ron's reputation among their peers, as punching a friend is not an acceptable behavior in most cases.
In some Harry Potter fanfiction, Ron's muscles might be emphasized in various ways. For example, in a story where the trio has to face a physical challenge, Ron could suddenly show off his unexpected strength due to his well - developed muscles. Maybe he has been secretly training during their time at Hogwarts, and this newfound strength helps them get out of a tight situation.
Luna Lovegood can also be a prominent character. She could have some unique insights about the strange lemon - related happenings. Maybe she's the one who first notices the significance of a lemon - shaped cloud that has some sort of magical connection, and she guides Harry and Ron in understanding it.
Often, their friendship evolves as they learn to understand each other's weaknesses. Ron realizes that Harry has a heavy burden as the Chosen One, and Harry comes to understand Ron's need for recognition. They support each other in these aspects, which helps their friendship to develop. For instance, when Ron is feeling overshadowed by Harry's fame, Harry makes an effort to include Ron in important matters more, and Ron starts to be more confident in his own abilities because of Harry's trust in him.
It could be a misunderstanding. For example, Ron might think Harry did something really bad to Hermione or their other friends. Without proper communication, his anger could lead him to punch Harry. Also, if there was some sort of magical influence or dark magic at play that affected Ron's judgment, that could be a reason too.
Highlight their shared interests. Both Harry and Ron love Quidditch. You could write a story where they train together intensively for an important Quidditch match. During the training, they support each other through setbacks, like when Ron misses a crucial shot or Harry falls off his broom. This shared experience would enhance their friendship.
Maybe Ron is jealous of Harry and wants to have something that belongs to him for a change. The cloak gives Harry a certain freedom and mystery, and Ron might be longing for that kind of experience.
Harry might be really angry with Ron and it could damage their friendship. They've been through a lot together, and stealing something as important as the cloak is a big betrayal.