Well, you could create an OC dragon slayer who was initially from a different dimension. In this dimension, the rules of dragon slayer magic are a bit different. They come to the Fairy Tail world and have to adapt their magic while also facing the challenges there. Maybe they have a special form of dragon slayer roar that can freeze time for a short period, which would be a really cool and unique ability in the context of Fairy Tail battles.
An interesting OC could be a dragon slayer who has a split personality. One personality is the typical brave and powerful dragon slayer, while the other is a shy and reserved side that comes out in certain situations. Their dragon slayer magic could also be affected by this split. For instance, when in the brave personality, their fire dragon slayer magic is stronger and more intense, but in the shy side, it becomes a more gentle, warm glow that can be used for healing rather than attacking.
One idea could be an OC Dragon Slayer who has the power of a unique dragon, like a crystal dragon. This slayer could use the dragon's power to create crystal-based attacks. Another idea is an OC who was trained by a dragon in a hidden realm and then enters the Fairy Tail world with a different set of values compared to the regular dragon slayers. Maybe they have a more pacifist view at first but gradually learn to fight when necessary.
Well, you could write about a new dragon slayer who has an elemental power that no one has seen before, like the power to manipulate light and shadow as a dragon slayer. This character could start as an outcast but then prove their worth in the Fairy Tail guild by using their unique powers to defeat powerful enemies. They could also have a special bond with a mysterious dragon that no one else is aware of.
One idea could be an OC dragon slayer who has the power of a rare and ancient dragon. Their magic could have unique side - effects or abilities that no one has seen before. For example, instead of just breathing fire like a typical fire dragon slayer, they could create a special type of fire that can heal as well as destroy.
One idea could be to create an OC (Original Character) who is an Element Dragon Slayer with a unique element, like shadow. The fanfiction could start with the character's discovery of their powers in a small, forgotten village. They then embark on a journey to find their dragon parent, facing various challenges along the way, including battles with dark guilds who want to use their power for evil.
One idea could be a slayer from a different dimension coming to the Fairy Tail world. This new slayer could have unique powers that no one in Fairy Tail has seen before, leading to all kinds of adventures and challenges as the guild tries to figure out how to deal with this new arrival.
Another plot could revolve around the origin of Dragon Slayer magic. Maybe a long - lost scroll is found that reveals secrets about how the magic was first created and what its true purpose was. This could lead the Dragon Slayers on a quest to find out more about their powers and their connection to the dragons.
Maybe the fanfiction could focus on a dragon slayer who loses their powers but then discovers a new way to regain them. For example, they might have to go on a spiritual journey and face their inner demons. Along the way, they form new bonds with the members of Fairy Tail, which helps them in their quest.
One idea could be to focus on the male OC's origin. Maybe he was found as an orphan by the ice dragon in a frozen tundra. The dragon raised him and taught him the ways of an ice dragon slayer. His journey could start with him leaving the dragon to explore the world, much like Natsu did in the original Fairy Tail story.
A great plot idea for a Fairy Tail God Slayer OC fanfiction is that the OC is actually a descendant of an ancient and powerful God Slayer. But this heritage comes with a curse that the OC has to break. Meanwhile, a powerful enemy from the past, who was once defeated by the OC's ancestor, is resurrected and is after the OC to get revenge. The OC has to rely on their friends in Fairy Tail and their own growing power to face this threat. Also, the OC could be framed for a crime they didn't commit in the magical world. They have to prove their innocence while also dealing with the fact that some gods want them dead because they are a God Slayer.
One interesting plot idea could be that the 5th generation dragon slayer has a unique type of dragon magic that is a combination of different elements. For example, they can control both fire and ice dragon slayer magic at the same time, which makes them a target for both good and bad forces in the Fairy Tail world. Another idea is that this dragon slayer has a connection to an ancient dragon prophecy that no one else is aware of. They have to figure out what their role is in this prophecy while also dealing with the normal challenges of being a dragon slayer in Fairy Tail.