One reason could be that Minerva sees Hermione as a kindred spirit. Hermione is highly intelligent and dedicated to her studies, just like Minerva was when she was younger. So, Minerva is possessive because she wants to nurture that part of Hermione and sees herself in her. It's like she wants to relive her own glory days through Hermione.
Perhaps Minerva is possessive because she realizes Hermione's potential to change the wizarding world for the better. She knows that Hermione has the brains and the drive, and she doesn't want anyone or anything to derail Hermione from that path. So, she's possessive in the sense of being a guardian, making sure Hermione stays on track to reach her full potential.
One possible reason could be envy. Maybe Fleur sees Hermione's intelligence and skills and feels threatened. So she becomes possessive to try and keep Hermione in a certain place or relationship where she can control her influence. Another reason might be that Fleur has some deep - seated insecurities. Hermione is well - liked and respected in the wizarding world, and Fleur, perhaps unconsciously, wants to claim Hermione as 'hers' to boost her own status. It could also be a case of misinterpreting friendship for something more possessive. If they are friends in the fanfic, Fleur might not know how to handle her strong feelings for Hermione in a healthy way and ends up being possessive.
One reason could be love. Draco might have fallen deeply in love with Harry and his possessiveness is a way of showing his strong feelings. He doesn't want to lose Harry to anyone else.
Love is a big reason. She loves Percy deeply and is afraid of losing him. In the world of the fanfiction, there could be many threats to their relationship, so she holds on tightly.
One reason could be that she lost so much time with Naruto due to her early death in the original story. So in the fanfiction, she's overcompensating for that lost time by being possessive.
One reason could be that he has deep feelings for her. He might not be used to having such strong emotions for someone and this possessiveness is his way of showing how much he cares.
Maybe it's because Hermione has unique qualities. Her intelligence and strength might attract James, and his possessiveness could stem from a fear of losing someone so special.
One possible reason could be that she sees Harry as a symbol of hope in the wizarding world. As a hero figure, Tonks might feel the need to protect and be possessive of him to ensure his safety for the greater good.
One reason could be that he sees something special in Sakura. Maybe he admires her strength or her kind heart, and he doesn't want to lose her to someone else who might not appreciate her as much as he does.
In the fanfiction, it could be that Jason has been through a lot with Percy. They might have shared many adventures and experiences that made Jason feel like he has a sort of claim over Percy. It could also be related to the world - building in the fanfiction. For example, if there are certain power dynamics or alliances that make Jason protective and possessive of Percy. Another aspect could be that the author wants to explore a complex relationship dynamic between the two characters, where Jason's possessiveness adds an interesting layer to the story.
One possible reason could be a deep emotional bond. Maybe Gaara has seen Naruto's unique strength and kindness, which makes her feel a strong connection. It could also be due to a sense of protection. Naruto might have been in situations where he was vulnerable, and Gaara's possessiveness is her way of ensuring his safety.