One interesting plot could be that female Zeref, with her knowledge of dark magic, tries to shield Natsu from the more dangerous aspects of the magic world while also teaching him how to control his own unique powers. Maybe she has a premonition of the great role Natsu will play in the future and wants to make sure he's ready.
A possible plot could involve female Zeref raising Natsu in a hidden location away from the rest of the Fairy Tail world. As Natsu gets older, he becomes curious about the outside world and starts to venture out. This could lead to all sorts of adventures where female Zeref has to protect him from both the natural dangers of the world and those who might be after Natsu because of his potential power. And along the way, Natsu could start to develop his own sense of right and wrong, which might not always align with Zeref's more morally ambiguous views.
Perhaps female Zeref, in raising Natsu, has to deal with the conflict of her own dark past and the purity she sees in Natsu. She could be constantly torn between her old ways and the new, more nurturing role. And as Natsu grows, he starts to question her motives, leading to a complex relationship full of mystery and discovery. For example, Natsu might discover some secrets about her past that make him question whether he should continue to trust her or not.
I'm not sure of specific 'female Zeref raises Natsu' fanfics off the top of my head. You could try searching on popular fanfic platforms like Archive of Our Own or Fanfiction.net. Just type in the relevant keywords and you might find some great stories.
Well, it depends on the specific fanfiction. Some might have a plot centered around their unique friendship in a different AU (alternate universe), like they team up to fight a common enemy. Others could explore their relationship in a more emotional way, perhaps with Zeref having to deal with her new female form and Natsu being there to support her in ways different from the original story.
One idea could be that baby Natsu has some sort of special connection to Zeref that even Zeref doesn't fully understand at first. Maybe Natsu's presence starts to change Zeref's dark thoughts a bit.
One plot idea could be that Zeref discovers a way to reverse his curse through Natsu. Since Natsu is his creation, there might be some hidden connection that could be explored. Maybe Zeref tries to use Natsu's unique dragon - slayer magic to break the chains of his dark magic.
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.
Well, one possible plot could be that Zeref kidnaps Natsu in an attempt to use his power for some dark purpose. Maybe he wants to turn Natsu into a weapon against Fairy Tail. Zeref might believe that Natsu's unique dragon - slayer magic can be harnessed in a way that no one else's can.
Well, perhaps Zeref kidnaps Natsu because he sees Natsu as a key to some grand plan. Maybe he wants to use Natsu's power for his own dark purposes. For example, Zeref might think Natsu's unique magic can help him break some sort of ancient curse or gain access to a powerful magic source.
Another idea for this fanfiction could be that they were both students at a very old and secret magic academy in the past. Zeref was an outcast because of her dark magic, but Natsu didn't care. He befriended her, and together they explored the secrets of the academy and the magic within it. However, their friendship was soon tested when the academy's elders discovered Zeref's true nature.
One interesting plotline could be a redemption arc for Zeref. In this, Natsu plays a key role in helping Zeref see the good in the world again. Maybe Natsu shows Zeref the value of friendship and family through his own relationships in the guild. This could lead to Zeref using his powers for good instead of his previous evil - doings.
One possible plot could be that Natsu, as an adult, takes on the role of a mentor to Mira. He could teach her new magic skills he has learned over the years. For example, he might share his unique fire - based combat techniques, which Mira could then adapt to her own magic style. This could lead to a series of adventures where they face powerful enemies together and Mira grows in strength and confidence under Natsu's guidance.