Well, if Natsu asks Lucy out in fanfiction, it could change the whole dynamic of the Fairy Tail group. Their friends would probably be super supportive, especially Happy. They could start exploring new places not just for quests but also for romantic getaways. And Lucy might write a new story about their relationship in her diary.
If Natsu asks Lucy out in fanfiction, it would be a big step for their relationship. Natsu, being the bold and passionate character he is, might do it in a very straightforward way. Lucy, on the other hand, might be initially shocked but then happily accept. This could lead to a lot of sweet moments like Natsu bringing her flowers from his travels and Lucy making special star - shaped keychains for Natsu.
In some fanfictions, if Natsu kidnapped Lucy, it could be a comical situation. Natsu might do it out of his own strange sense of protecting Lucy in an overzealous way. Maybe he thinks there's a danger that only he can keep her safe from, and his impulsive nature leads him to this 'kidnapping' which is more like a forced protection.
In fanfiction, during their alone time, Natsu and Lucy might simply have a deep conversation. They could talk about their dreams, like Natsu sharing his desire to find Igneel more in - depth, and Lucy might open up about her hopes for her Celestial Spirit magic to grow stronger.
Another possibility is that they get into a bit of a light - hearted argument over something silly like who has the better taste in food. But in the end, they would just laugh it off and realize how much they enjoy each other's company during this alone time.
His friends would most likely try to heal him immediately. Wendy, with her Sky Dragon Slayer magic, could be the first to attempt to close his wounds and stop the bleeding. She has great healing abilities, so she would be crucial in this situation.
In a fanfiction, there could be a situation where Lucy is forced to side with a group that Natsu is against. This would make Natsu see her as an enemy. Or perhaps there is a prophecy that Lucy is involved in that Natsu misinterprets as something bad. He might think she is a threat to the guild or his friends. Also, if there is a love triangle situation where Lucy chooses someone else over Natsu in a way that really hurts his feelings, that could be a reason for him to start hating her.
Natsu could end up teaming up with some unexpected allies from Tartaros. Maybe there are some members who have a change of heart and decide to help Natsu fight against the more evil elements within their own organization.
She could be a key figure in an ancient prophecy. For example, the prophecy might state that only the son of a certain dragon - slayer mother (Natsu's mother) would be able to defeat a great evil that threatens the Fairy Tail world. This would set Natsu on a path to discover his mother's identity and fulfill the prophecy.
Well, one possibility could be that it's a really innocent situation. Maybe they got into some kind of magical mishap that made them dirty and the only available place to clean up was a shared shower area. But they're both really embarrassed and trying to be respectful of each other's space while also dealing with the comical aspect of the situation.
One possible plot twist could be that Lucy initially refuses Natsu's proposal because she fears it will change their dynamic in the guild. She might think that getting married will make them less focused on their adventures and more on domestic life.
One possibility is that their child inherits Natsu's dragon - slayer magic and Lucy's celestial spirit magic. Maybe the child uses this unique combination to protect Fairy Tail from a new, powerful enemy.