One possible plotline could be Natsu trying to prove his innocence. Maybe he was wrongly accused of a serious crime within the Fairy Tail guild, like endangering the lives of other guild members during a mission. He then sets out on a journey to find evidence that clears his name while also facing various challenges and enemies along the way.
Another plotline might involve Natsu being expelled as part of a grander conspiracy. For example, an enemy of Fairy Tail might have framed him in order to weaken the guild. Natsu, while expelled, discovers the conspiracy and teams up with some former guildmates who believe in him to take down the real villains and earn his way back into the guild. It could involve a lot of action, magic battles, and some emotional moments as Natsu struggles with being cast out from the place he considered home.
It could also be a story about Natsu's personal growth during his exile. Without the support of his Fairy Tail friends initially, he has to rely on his own strength and wits. He might discover new magical abilities or face challenges that test his character, and in the end, he either returns to Fairy Tail as a changed and stronger wizard or decides that his new path outside the guild is better for him.
One possible reason could be that he accidentally causes too much destruction during a mission. Maybe he loses control of his magic and wrecks an important place in the magical world, leading the guild to expel him as a form of punishment.
One possible plotline could be that Lucy uses her charm and intelligence to plan elaborate schemes to get Natsu's attention. For example, she might invite him on special adventures that are just for the two of them, where she can show off her skills and bond with him more deeply. Another could be that she gives Natsu special gifts that are meaningful to him, like a scarf she made herself which has some magical protection. Or perhaps she starts dressing in a way that she knows Natsu will find appealing, not in a vulgar way but in a way that highlights her beauty and confidence.
One possible plotline could be that the other Fairy Tail members set up a series of pranks on Natsu, like replacing his fire - based spells with something silly, like making his hands shoot out confetti instead of flames. Another could be that they constantly make jokes about his fear of transportation, especially his motion sickness on vehicles.
It could be a rival wizard from another guild. This wizard might be jealous of Natsu's power and popularity within Fairy Tail. So, they fabricate evidence to get Natsu expelled, aiming to not only remove him as a competitor but also to create chaos within Fairy Tail. They could continue to be a thorn in Natsu's side as he tries to clear his name and get back to the guild.
Perhaps a plotline where an outside force tries to manipulate Natsu and Zeref against each other while they are in Fairy Tail. This could lead to a lot of internal conflict within the guild as members take sides. But in the end, through the power of friendship and the values of Fairy Tail, they see through the ruse and become stronger together, uniting the guild even more firmly.
It could be that the baby is related to someone from Natsu's past. When he finds the baby, he feels an instant connection. He then embarks on a journey to find out more about this connection, all while ensuring the baby's safety. Along the way, he might learn more about his own history and family through the baby.
One possible plotline could be that the guild goes into deep mourning. Gray might feel a special sense of loss as they were rivals but also close friends. Lucy could be devastated and vow to find a way to bring Natsu back, perhaps by seeking out powerful magic or ancient spells. The guild could also face a new threat that they struggle to deal with without Natsu's strength.
One interesting plotline could be Natsu and Juvia teaming up for a difficult mission. They have different magic styles, Natsu with his fire magic and Juvia with her water magic. Their interaction during the mission, like Juvia being a bit shy around Natsu at first but then growing more confident as they face challenges together, can make for a great story.
One interesting plotline could be Natsu coming back with new and powerful magic. For example, he might have learned some ancient spells during his time away. Another could be his reunions with the various members of Fairy Tail. He would have emotional moments with Lucy, Happy, and the others, reminiscing about old times and looking forward to new adventures together.