Some writers characterize Acnologia as a misunderstood loner. They show that his actions of destruction are a result of his past traumas. Others might make him more of a power - hungry villain who just wants to rule over all. There are also those who give him a sense of humor, which is a very different take from his usual brooding and menacing self in the original series.
Well, adapting to Acnologia's body could be a complex process. They would have to learn how to control the raw power within it. This power might be overwhelming at first, and they could accidentally cause destruction. To adapt, they might start by testing their limits in isolated areas. Emotionally, they would also have to come to terms with the fact that they are now in the body of a feared being. They might try to use their memories of Fairy Tail to bring out the good in this new form, like using Acnologia's strength to protect the weak as they did in their previous life.
In some fanfictions, Acnologia is made out to be Natsu's father. But this is not part of the original canon of the Fairy Tail series. Fanfiction writers often like to create such unexpected family relationships to add new twists to the story.
In some fanfictions, Zeref is portrayed as a more sympathetic character. Instead of just being the big bad, he might be shown as a victim of his own power or circumstances. For example, he could be a character who was forced into doing evil things and actually has a good heart deep down.
One possibility is that Naruto, with his determination, could adapt Zeref's powers in a unique way. Maybe he'd use Zeref - like magic to enhance his ninjutsu. For example, he could infuse Zeref's death - based magic into his Rasengan, creating a more powerful and dangerous attack. Another aspect could be Naruto's personality change. If he becomes influenced by Zeref, he might become more brooding and less of the cheerful ninja we know. However, his core values of friendship and protecting the village would still likely be there, just warped a bit by Zeref's dark nature.
Yes, there are likely some fanfictions out there with this concept. You can try searching on popular fanfiction websites like FanFiction.net or Archive of Our Own. Just type in 'Naruto Brother of Zeref' in their search bars and see what comes up.
It could mean that in a Naruto fanfiction, the character Acnologia from another series has been incorporated into the Naruto universe. Maybe the writer wanted to create an interesting crossover by bringing in this character's unique traits or powers into the Naruto - inspired story.
One popular female Acnologia fanfiction might be those that explore her backstory. For example, there could be a fanfic that delves into her early days as a dragon slayer and how she became the powerful being she is. It might show her training, her relationships with other dragon slayers at that time, and the events that led to her transformation into a more menacing figure.
In many Fairy Tail fanfictions, the battle between Natsu and Acnologia is often depicted as extremely epic. Natsu's fiery determination and his unique dragon - slayer magic make for an interesting contrast against Acnologia's overwhelming power. Some fanfictions might have Natsu discover new forms or powers in order to stand a chance against the fearsome Acnologia.