Definitely wrong. Fanfiction based on a diary is likely to contain a lot of personal and emotional content. Natsu should respect Lucy's privacy and not read it without her permission. If he does read it, it could damage their relationship and trust.
One common theme is secrecy. Since it's about Lucy's diary, there's often an element of secrecy involved, like Natsu finding the diary by accident and having to keep it a secret. Another theme is the deepening of their relationship. As Natsu reads the diary, he gets to know Lucy on a deeper level, which brings them closer.
Well, it really depends on what you consider 'good'. Some might be more focused on the romantic aspect between Natsu and Lucy, while others could have more of an adventure plot with the diary as a key element. I'd recommend checking out the reviews and ratings on the fanfiction platforms to find ones that are highly regarded.
One possible plotline is that Natsu starts writing in the diary about his confusion regarding his feelings for Lucy. He might write about how he gets jealous when other guys show interest in her. Another plot could be that Lucy accidentally discovers the diary and confronts Natsu about it, which then leads to them finally admitting their feelings for each other.
He might be really surprised. Since Lucy's diary fanfiction could contain her most private thoughts and feelings, Natsu would get a peek into a side of Lucy he may not have known before.
Well, 'natsu loves lucy' is a common theme in fanfiction, especially in the context of the Fairy Tail series. A diary - style fanfiction might be really interesting. It could be written from either Natsu's or Lucy's perspective. For example, if it's from Natsu's perspective, it might detail his growing feelings for Lucy day by day, how he notices the little things about her like the way she smiles when she's reading a book or how she gets excited when they go on a mission together.
One aspect of their married life in fanfiction could be the domestic side. Lucy might try to get Natsu to be more organized at home, while Natsu would bring his energetic and fun - loving nature into their household. They would probably have a lot of cute and comical moments, like when Natsu accidentally burns the dinner and Lucy just shakes her head and laughs it off. Their love would continue to grow as they share these everyday experiences.
One reason Natsu gets jealous of Lucy in fanfiction could be that he sees her as his special person. He's used to having her attention, so when someone else gets it, he gets jealous. For instance, if she goes on a mission with someone else instead of him.
They can develop their relationship by having small, everyday moments. For example, sharing breakfast together as a family, where they talk about their plans for the day. Natsu could show his love for Lucy by being more protective of her and their family in dangerous situations. Also, they could have inside jokes that only their family understands, which would strengthen their bond.
One character that would be interesting to include is Mirajane. She has a motherly and observant nature. She could be the one to nudge Natsu and Lucy in the right direction when it comes to their relationship. For instance, she might arrange for them to go on a mission together that she knows will bring them closer. Laxus could also be in the fanfiction. His powerful presence can create a sense of danger or protection. If there's an outside threat to the guild while Natsu and Lucy are exploring their relationship, Laxus could be at the forefront of defending the guild, which would impact Natsu and Lucy's situation. And don't forget about Cana. She could be the one to create some light - hearted chaos, like daring Natsu and Lucy to do something that ends up bringing them closer, such as a bet that leads to a shared adventure.
As they travel, their bond deepens. They start to rely on each other more. Natsu becomes more protective of Lucy, and Lucy begins to understand Natsu's impulsive nature better.