Maybe there's an ancient artifact in the guild's basement that Natsu accidentally activates. It backfires and turns him into a baby. The guild then has to work together to find a solution. Happy could act as a sort of guide for baby Natsu, trying to communicate with him in his own way. Natsu as a baby might also show some new, innocent sides of his personality, like being fascinated by simple things like shiny objects or the guild's pets.
One possible plot could be that the magic in the world goes haywire. Natsu is caught in a spell that turns him into a baby. His friends in Fairy Tail are shocked at first. Lucy might take on the role of a caretaker, trying to figure out how to reverse the spell while also dealing with a baby Natsu's unpredictable behavior like randomly using small bursts of fire magic that are more like cute little puffs now.
Well, perhaps there's a dark mage who creates a new kind of curse. Natsu is the unlucky target and is transformed into a baby. Gray would probably be both amused and worried. They would have to search for a rare magical item to turn Natsu back. Meanwhile, baby Natsu might start to bond with the guild members in a different way, like clinging to Erza and making her more maternal than her usual tough self.
Maybe in the fanfiction, Natsu's emotional state causes him to turn into a dragon. After a great loss or a fit of extreme rage, his magic reacts and he transforms. This new form is both a blessing and a curse. It gives him the power to protect his loved ones better but also isolates him as he struggles to understand and control his new dragon instincts.
One possible plot could be that Natsu, after being hit by a strange magic spell during a battle, turns into a girl. His friends are initially shocked but quickly adapt. Natsu, as a girl, discovers new aspects of his own personality. For example, he might find that he is more in touch with his emotions. He could also face some challenges like having to deal with different clothing styles and the way others now perceive him. As the story progresses, he tries to find a way to break the spell while still learning important lessons about himself and his relationships with others.
Well, one possible plot could be that the other characters in the story are initially shocked. Papyrus might be super confused but also determined to take care of his 'baby' brother. They could go on little adventures where Papyrus has to protect Sans from various threats in the Underground while also trying to figure out how to turn him back to normal.
Well, the plot could involve his teammates having to take care of him. They might struggle at first because Kuroko as a baby can't communicate in the same way. Maybe they have to figure out his needs like when he's hungry or sleepy. And they could also try to keep it a secret from the other teams to avoid any distractions during games.
The story could start with some sort of strange experiment gone wrong that turns Junkrat into a baby. The rest of the crew is shocked at first. Mei could use her scientific knowledge to try and find a way to reverse the process. Meanwhile, Reinhardt might tell stories to baby Junkrat about their adventures, as if he can understand. And Lucio could play some soft music to keep the baby calm.
Perhaps in this fanfiction, when Natsu becomes an adult, he decides to explore different parts of the magical world that he was previously unable to reach. He could discover new types of magic or encounter different magical creatures. This could lead to him bringing back new knowledge to his guild, and they could use it to strengthen themselves. Also, his transformation might make him more of a leader figure within the guild, guiding the younger members.
Another plot could be that the baby's arrival changes their relationship dynamic. Before, they were mainly focused on their individual growth and the guild. But now, they have to work together as a couple and as parents. They might argue at first about how to raise the baby, like Natsu wanting a more adventurous upbringing while Mirajane prefers a more stable and safe environment. But in the end, they find a middle ground and their relationship becomes stronger.
Well, perhaps in the fanfiction, Natsu and Lisanna discover they're having a baby unexpectedly. They then have to adjust their lives as members of Fairy Tail. Lisanna might worry about how her pregnancy will affect her ability to go on missions. Natsu, on the other hand, vows to be the best father and to keep his family safe from any threats that may come their way, be it from dark guilds or other magical creatures.
The plot might involve Natsu and Mirajane finding a baby dragon in the form of a human baby. Since Natsu has a connection with dragons, he feels a special bond. Mirajane, with her kind heart, steps in to help raise it. They face challenges like protecting the baby from dark guilds who might want to use the baby's power.
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.