The 'natsu dark past secret fanfiction' might revolve around Natsu's family. There could be some dark secrets about his family that he has just discovered. Maybe his family was involved in some sort of dark magic or a feud with another powerful group, and Natsu is now starting to uncover the truth about it.
It could be someone from Natsu's past. Maybe an old rival who knows about his dark secrets and wants to use them against him.
Well, it could be things like a tragic family history. Maybe Natsu's family was involved in some sort of dark magic that got them in trouble. Another possibility is that Natsu had a past encounter with a powerful and evil entity that left a mark on his psyche.
Another plot twist could be that the past they remember isn't actually real. It was all an illusion created by a powerful mage. When they find out, they have to figure out who the real enemy is and why they were put in this false past. This would completely shift the focus of the fanfiction from their relationship in the 'past' to finding out the truth behind the illusion.
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.
It could be about Natsu finally opening up about a tragic event from his childhood that shaped his personality. Maybe it involves the loss of a loved one, or an experience that made him distrust a certain group of people.
It could make him seem more vulnerable. Usually, he might come across as strong and fearless, but revealing his dark past shows he has his own insecurities and traumas.
Perhaps the secret is that Lucy has a unique magical item that is very powerful and dangerous. Natsu keeps it a secret because he doesn't want other mages in Fairy Tail to get greedy or misuse it. This item could be something that was passed down in Lucy's family and she doesn't fully understand its potential yet.
Well, one possible plot could be that Natsu, after some sort of betrayal in Fairy Tail, decides to create his own dark guild. He might gather some disgruntled mages who also feel wronged by the mainstream guilds. Their goal could be to change the magic world's power structure in a more radical way, using darker forms of magic that are usually shunned. For example, they could explore ancient and forbidden magic spells to gain an edge over other guilds.
One plot twist might be that the source of Natsu's time - becoming ability is actually a dark force. He initially thinks it's a great power, but as the story progresses, he discovers that it's slowly corrupting him or has some hidden and dangerous agenda. This could lead to an internal struggle within Natsu as he tries to either control or get rid of this power. Another twist could be that time - based changes Natsu makes end up creating an alternate reality that he has to fix before it's too late.
A plot could be that Natsu and Lisanna have been longing for a baby. They go through a magical ritual in their guild to increase their chances of having a child. Once Lisanna becomes pregnant, the whole guild gets involved. Everyone is excited and offers their help. Natsu becomes super protective of Lisanna and the unborn baby. There could be a sub - plot where an enemy tries to target Lisanna because of the powerful baby she is carrying, and Natsu has to fight to keep them safe.