One idea could be that the OC is a new duelist in the Yu Gi Oh world. They accidentally stumble upon a powerful artifact while exploring an ancient temple. The Dark Magician Girl senses this and approaches the OC. Together, they have to face off against an evil force that wants to steal the artifact for its own dark purposes.
Well, this clumsy magician might be so bad at his hand movements that when he's supposed to make a card disappear, he actually drops all the cards on the floor. And then, while trying to quickly pick them up, he accidentally steps on a few and slips, landing in a heap of cards and embarrassment. His attempts to get back up gracefully only end up with him getting more tangled in his cape. It would be a really comical sight for the audience.
One idea could be a story where the Dark Magician and Celtic Guardian team up to face a powerful, ancient evil that threatens their world. They start off as unlikely allies, with the Dark Magician being more of a solitary and mysterious figure, while the Celtic Guardian is a brave and straightforward warrior. As they journey together, they learn to respect each other's strengths and overcome their differences to defeat the foe.
One idea could be that they have to team up to face a powerful new enemy that is threatening the magical world. They might discover a long - lost spell during their adventure.
Another interesting one is 'Strategic Magic Unleashed'. The OC in this fanfiction is a young magician who discovers new ways of using strategic magic. It has some exciting battle scenes where the magician's strategic thinking gives them an edge. It also explores the relationships between different magical beings in a very engaging way.
The uniqueness often lies in the character. Since it's an OC (original character), the author can create a magician with a completely different set of skills and personality compared to existing ones. For example, they might have a special way of strategizing that sets them apart.
Another possibility is a story in which a young wizard in the Harry Potter world discovers a hidden portal that leads to the dimension where Doctor Strange operates. This wizard, inspired by Strange, begins to study a new form of magic that combines the principles of both universes. They then return to Hogwarts and start to teach their friends this new hybrid magic, which causes quite a stir among the faculty and students alike.
A good fanfiction might involve an OC that is a descendant of an ancient magician family in the Arc V world. This OC has a special connection to the Dark Magician. The story could explore how this connection develops over time. The OC might use the Dark Magician in a different way than traditional duelists, perhaps using it more as a guide or a source of ancient magic knowledge rather than just a card in a duel.
One idea could be exploring the backstory of a minor character in more detail. For example, a sidekick of Sonea who has their own secret magical abilities that they've been hiding. This could add a new layer of mystery to the story.
A fanfiction could explore the backstories of the Dark Magician and Celtic Guardian. Maybe they have a shared history that has been long forgotten. The story could unfold as they gradually remember their past connection and how it impacts their present relationship.