Well, the fanfiction could start with Natsu finding out he has a daughter he didn't know about. Maybe she was the result of some long - lost adventure or a situation he was in and forgot due to a spell or something. His daughter could have a unique blend of magic, not just fire - dragon slayer magic. She could also have some other latent abilities. The story could then focus on Natsu trying to bond with his daughter, teaching her about the values of Fairy Tail, like friendship and loyalty, while they also face threats from old enemies who see the daughter as a new target.
Another possibility is that the kid is from an alternate dimension where time passes differently. Natsu's kid shows up in the Fairy Tail world and he has to figure out how to be a father. The story could focus on their journey to get to know each other and the kid's adjustment to this new world.
She would fit in very well. The Fairy Tail guild is all about family and acceptance. Given her parents are Lucy and Natsu, she'd be welcomed with open arms. She could learn from the older members like Makarov and Mirajane, and bond with the younger ones like Romeo. Her magic skills would also contribute to the guild's strength during battles or when helping the town.
Yes, in a lot of Fairy Tail fanfiction, Natsu can be overpowered. Writers often like to amp up his powers for more exciting storylines. For example, they might give him new fire - based abilities or make his existing ones even stronger to defeat more powerful foes.
In fanfiction, Natsu's age can vary greatly. Some authors might keep him at his canonical age from the original Fairy Tail series, which is around 17 - 18 years old at the start. However, in alternate universe fanfictions, he could be older or younger depending on the plot. For example, in a time - travel based fanfic, he could be much older if the story takes place far into the future or much younger if it goes back to his childhood days.
One possibility is that their daughter has a special ability to combine Natsu's fire magic and Lucy's summoning magic in unexpected ways. For example, she could summon a fire - based celestial spirit. She might grow up in a Fairy Tail that has changed a bit since her parents' time, with new members and new challenges. She could be mentored by some of the older guild members like Erza or Gray. And as she comes of age, she might discover secrets about her family's past that put her in a position to make important decisions for the future of the guild and the magical world at large.
Well, in the 'natsu has fallen protecting fairy tail fanfiction', it might show Natsu facing an overwhelming threat. Maybe it's a dark wizard or a horde of demons. He puts his life on the line to safeguard Fairy Tail, the place he loves and his friends there. His fall could be the catalyst for other characters to grow stronger, to avenge him or to carry on his legacy within the guild.
In this kind of fanfiction, the kid might have some unique abilities. Since Natsu is a dragon slayer, the kid could have an enhanced form of dragon slayer magic or a combination of different magics. For example, the kid could have the ability to not only use fire like Natsu but also manipulate wind to make the fire more powerful.
One possible aspect of a Fairy Tail Natsu and Tartaros fanfiction could be Natsu's battle against the powerful foes in Tartaros. He might face new and terrifying enemies that test his limits. His dragon slayer magic would be put to the extreme, and perhaps he discovers new powers along the way.
In fanfictions like this, the character development of Natsu within the context of Sabertooth is interesting. He could learn new magic techniques from them or teach them his own unique brand of Fairy Tail spirit. It might also explore how the different cultures of the two guilds clash or blend.