Gray could be one. Since he and Natsu have a long - standing rivalry, Gray might try to bring Natsu back to Fairy Tail. He'd be conflicted between his annoyance with Natsu and his concern for his former guildmate.
His friends could be involved. For example, Lucy might stumble upon some old records or meet someone who knew Natsu in the past. Gray could also be part of it, especially if it has something to do with the magic world's secrets that they both are a part of.
One popular 'natsu is dark fanfiction' might be those that explore Natsu's inner turmoil in a more sinister way. For example, a story could depict him being corrupted by a dark magic that changes his personality. He might become more aggressive towards his friends, not out of true malice but because of the influence of the dark power. This can create a lot of conflict and drama within the Fairy Tail universe.
The main characters are obviously Natsu and Mirajane. Natsu, who has a dark side in this fanfiction concept, is known for his fiery magic and impulsive nature. Mirajane, on the other hand, is a powerful mage with her demon form capabilities.
One interesting 'dark natsu nalu fanfiction' story could be about Natsu and Lucy facing a powerful dark magic that is corrupting their world. In this story, Natsu's dragon powers are affected in a strange way, and Lucy has to use her celestial magic in innovative ways to save them both.
He might lose his friends at Fairy Tail. Since Fairy Tail is all about friendship and light, joining a dark guild would put him at odds with his former comrades.
One popular storyline could be them going on a dangerous mission together. In this type of fanfiction, they might face powerful enemies and have to rely on each other's skills. Dark Natsu's more unpredictable power and Erza's strategic combat skills would make for an exciting combination. Another could be a story where Dark Natsu is in some sort of trouble and Erza has to help him out, which could explore their relationship in a different way. And then there are also fanfictions that focus on their potential romantic relationship, showing how they might fall in love despite their differences.
There are a few authors that stand out. One author, let's call them [X], has a knack for writing emotional and in - depth stories about Dark Natsu and Erza. Their fanfictions often focus on the psychological aspects of the characters, which makes for a very interesting read. Then there's [Y], who is known for creating really complex storylines. In their works, Dark Natsu and Erza are often faced with difficult choices that really test their relationship. And of course, [Z] is popular for writing more light - hearted fanfictions with a lot of humor, still maintaining the essence of Dark Natsu and Erza's relationship.
Well, 'A Dark Natsu and Lucy Adventure' is a popular one. In this fanfiction, Natsu's dark side gets accidentally unleashed during a mission, and Lucy has to figure out how to deal with this new, more unpredictable Natsu. Then there's 'Darkness Within Natsu' where the story focuses on how Lucy tries to understand the source of Natsu's darkness and bring him back from the brink. 'The Dark Natsu - Lucy Alliance' is also quite good, as it shows them teaming up in a world filled with new and dark threats.
Well, aside from the well - known FanFiction.net and AO3, some niche anime - related forums might also have 'Dark Natsu and Lucy fanfiction'. However, these might not be as well - organized as the big platforms. Another option could be Wattpad, although it has a broader range of content, but you can still find some great 'Dark Natsu and Lucy' stories there if you search thoroughly.