A great fanfiction concept could be centered around Team Natsu getting magically separated. Natsu ends up in a realm where there's no fire magic, and he has to learn to adapt and find a way back to his friends. Gray could be in a world of eternal ice and has to find a way to break free. Lucy might be in a place where celestial spirits are feared and hunted, and she has to protect them while trying to reunite with the team.
One idea could be exploring Natsu's struggle to control his dragonized form. Maybe he accidentally dragonizes at an inopportune time and has to deal with the consequences, like scaring his friends or causing destruction. Another could be a scenario where he dragonizes to save the guild from an extremely powerful enemy that no one else could defeat.
Perhaps Natsu has a secret friendship with a character from another guild. They meet in secret and exchange valuable information or magic items. This could add an interesting layer to his character. Also, what if Natsu secretly has a connection to a powerful and ancient dragon that no one in the guild knows about? It could lead to some epic storylines.
Maybe in the fanfiction, Natsu has a different backstory. Instead of being raised by Igneel, he could be raised by a dark wizard, which would make his character more morally ambiguous and lead to a whole new set of story arcs where he struggles between the dark influence and the good in his heart like the relationships he forms with the Fairy Tail members would be very different as they try to sway him to the side of good.
One idea could be a mission where Natsu and Laki are paired up by accident. Laki, being more of a support - type mage with her wood - based magic, could initially be intimidated by Natsu's brash and powerful fire magic. But as they face challenges together, she learns to stand up to him and they develop a mutual respect. For example, they might encounter a powerful earth - based monster that is immune to Natsu's fire. Laki's ability to manipulate the surrounding trees to entangle the monster gives Natsu the chance to figure out a new strategy to defeat it.
One idea could be that Natsu is exiled due to a false accusation of using dark magic. He then has to journey alone to prove his innocence, encountering new friends and foes along the way. Maybe he discovers a new form of magic during his exile.
One idea could be Natsu going on a solo mission to a far - off land that has a different type of magic entirely. He has to learn to adapt and control this new magic to complete his task. Another could be Natsu training a new generation of Fairy Tail wizards, passing on his unique brand of magic and combat skills.
One idea could be that Mystogan and Natsu have to team up to face a powerful dark wizard. Since Mystogan is usually more reserved and Natsu is hot - headed, their clashing personalities could lead to some humorous and intense moments during the fight.
One interesting plot idea could be Natsu going on a special quest with each member of his harem separately. This would allow for character development of both Natsu and the individual harem members. For example, when he's with Lucy, they could discover a new type of celestial spirit magic that only works in a specific, long - lost realm. Another idea is that an enemy targets Natsu's harem to get to him, so he has to protect them all while also dealing with his growing feelings for each of them.
In this fanfiction, Natsu could discover that his abandonment was part of a bigger plan within Fairy Tail to protect him from a greater threat. He might initially be angry and resentful, but as he uncovers the truth, he has to decide whether to forgive his old guild or not. He could also meet other characters who were also once abandoned and form a bond with them to face the challenges together.
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.