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.
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.
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.
The theme of unrequited love can also be common in some 'lucy loves natsu fanfiction'. Maybe at the start, Natsu doesn't realize Lucy's feelings or is too focused on other things like his next adventure or his training. This creates a lot of tension and drama in the story, as Lucy tries to hide or express her feelings while Natsu is oblivious.
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.
The chemistry between Natsu and Lucy is full of potential for interesting stories. In fanfiction, authors can take that chemistry and develop it in different ways, like exploring what if Natsu realizes his love in a different situation. Also, their personalities are so distinct yet complementary, which makes for great storytelling in fanfiction.
Well, in some fanfictions, it could be through a dangerous situation. Maybe Lucy is in peril and Natsu's intense fear of losing her makes him realize his love. For example, if she's captured by a powerful enemy, Natsu's desperation to save her and the way his heart races at the thought of her being hurt could be the trigger.