In this fanfiction, it might be that there are secrets from Natsu's past that Erza discovers. These secrets could be related to some dark magic or a connection to a dangerous group. Erza, being the strict enforcer of the guild's rules, feels she has to distance herself from Natsu, which he takes as betrayal. This could then explore how their relationship evolves as Natsu tries to prove his innocence and Erza grapples with her loyalty to the guild and her feelings for Natsu.
Well, perhaps Erza was tricked into believing something false about Natsu. Maybe she was misled by some enemy who made it seem like Natsu was going to endanger the guild. So, in her sense of duty to protect the guild, she took actions that Natsu perceived as betrayal.
It could be that there was a misunderstanding about a powerful magical item. Natsu found it first, but Erza thought he was going to use it for the wrong reasons. She then tried to take it from him forcefully, which Natsu saw as a betrayal of their friendship. This would lead to a rift between them and a whole lot of drama in the fanfiction.
One possible reason could be a misunderstanding within the guild. Maybe some false information was spread about them, leading others in Fairy Tail to turn against them. Another reason might be a power struggle. If Natsu and Erza were becoming too powerful, some jealous members could have conspired to make it seem like they were betraying the guild. Or perhaps an outside force manipulated the situation to drive a wedge between them and the rest of Fairy Tail.
Maybe in this fanfiction, there are some artifacts or powers that both Naruto and Erza are after. Erza betrays Naruto to get her hands on this power first. This could set off a chain of events where Naruto has to find a way to stop her from misusing the power. It could also make Naruto question his own judgment in trusting her in the first place.
One possible plot could be that they discover the pregnancy and then face challenges together. Maybe they have to deal with the reactions of their friends in the guild, some being happy and supportive while others might be worried about how it will affect their adventuring lives.
Perhaps in the fanfiction, Natsu meets Erza in a completely new setting, like a parallel universe where the Fairy Tail guild doesn't exist yet. They start off as strangers but quickly realize they have similar goals. Erza might initially be a bit distrustful of Natsu's wild ways, but as they face challenges together, such as a group of bandits attacking a village, they learn to trust and rely on each other.
One possible plot is that a time - travel or alternate - reality situation occurs where Natsu and Erza are already married and have a baby. The story could show how they adjust to this new family life. Natsu might be the fun - loving dad who plays with the baby using his fire powers in a safe way, while Erza is the strict but loving mom who makes sure the baby is well - behaved and learns proper values. They would also have to deal with the reactions of their friends in the guild, some of whom might be shocked or overly excited about the new addition to their family.
It could be about a misunderstanding. Maybe Natsu is under a lot of stress or has been wrongly accused, and Erza's actions or words accidentally trigger his outburst.
Perhaps Makarov, the guild master, could be a part of the story too. He might be the one who has to deal with the consequences of this betrayal within the guild. His wisdom and leadership would be put to the test as he tries to keep the guild together while Natsu and Erza are at odds.
Perhaps she is betrayed in a romantic sense. She falls for someone who then turns out to be using her for their own gain, like getting closer to powerful members of the guild through her. This would shatter her trust in love and make her more guarded in future relationships.
One possible plot could be that Natsu and Erza are sent back in time to a crucial moment in the history of their guild. Maybe they go back to the time when the guild was first founded. They could end up having to protect the founders from a threat that was long forgotten in their own time. This would give them a chance to see how the guild started and also change some things for the better in the present.
Well, it could be about a powerful encounter. Maybe Erza initially mistakes End Natsu for the regular Natsu and there's some confusion. Then they might have a fight as Erza is always ready to combat threats. But as they engage, they could discover things about each other that change their views.