In terms of the overall plot, it could lead to a race against time. The characters will need to find a way to exorcise Vecna from Will quickly. This might involve seeking out new knowledge, perhaps from an unexpected source. Maybe an old character from the past who has some knowledge about Vecna's possession returns to help. It also opens up the possibility for new alliances and betrayals within the group as they struggle with this new situation.
It can introduce a sense of drama. When Gohan gets hurt, it makes the readers worry about his fate. This can create suspense as they wonder if he will recover in time to face future challenges.
The injury could introduce new characters. Maybe a healer Wesen shows up to help Nick. This new character could bring in new plot elements and relationships. Also, it might change Nick's perspective on his role as a Grimm. He could start to question if he's putting himself in too much danger and how it affects those around him. This internal conflict can drive the storyline in different directions.
Well, it could completely change the dynamic of their relationship. Firstly, they would have to deal with the responsibilities of impending parenthood. Natsu, being his impulsive self, might have to become more responsible. Lucy, on the other hand, would probably be more cautious about her actions as she has a life growing inside her. This event could also change their relationships with their friends in the guild. Their friends would likely rally around them, but there could also be some who might be shocked or even a bit envious. It could also lead to new story arcs, like how they prepare for the baby, finding a safe place to raise it, and what kind of parents they would be.
If Naruto gets cheated on by Sasuke in a fanfiction, it could greatly disrupt the traditional bond between them. It might lead to Naruto feeling betrayed and could potentially make him more cynical. This could change the direction of the story, perhaps leading Naruto to focus more on his own self - growth rather than their relationship.
It depends on the creativity and plot of the fanfic author. Sometimes they might introduce such a twist, but not always.
It can make the storyline more intense. The other characters will be in a rush to save her, and this can create a lot of drama.
Well, a frequent theme is the change in Dipper's personality. When possessed, he could become more aggressive or withdrawn, which creates a contrast to his usual curious and determined self. There may be a theme of redemption too. If Dipper does something bad while possessed, the story could be about him making amends once he's free. And sometimes, the fanfiction might use the possession as a way to introduce new powers or abilities that Dipper has to learn to control.
A common theme is the battle for control. Harry is constantly fighting against the possessing entity for control over his body and mind. For example, in many fanfictions, he tries to resist using dark magic that the entity might force him to do.
Peter's injury can change the whole dynamic of the story. It can slow down the action as everyone focuses on his recovery. This gives the writer a chance to explore more of the characters' relationships.