Maybe the OC is from a different dimension. Kitty Pryde discovers this when some strange energy readings occur. The OC has a different view on mutants and their place in the world. As Kitty helps the OC adjust to this new world, they develop a deep bond. Their relationship is tested when the OC's dimension tries to pull them back.
A more romantic plot could be that they meet by chance in a neutral zone between their respective universes. They initially clash due to their different personalities but gradually fall in love as they discover they have more in common than they thought. This could involve them learning about each other's pasts and how they became the heroes they are.
One idea could be that Naruto is somehow transported to the X - Men universe where he meets Kitty Pryde. They could team up to fight a common enemy, like a new villain who has the ability to steal chakra and mutant powers. Naruto could teach Kitty some of his ninja techniques, and Kitty could show Naruto how to use her phasing ability in creative ways during combat.
One idea could be that they meet through some magical cross - over event. Maybe a spell gone wrong transports Kitty to the Harry Potter universe. They initially misunderstand each other due to their different worlds' cultures but then gradually fall in love as they discover their shared values like bravery and loyalty.
The theme of self - discovery can also be present. Kitty Pryde is a character who has grown and changed over time in the comics. An oc x kitty pryde fanfiction could have both characters learning more about themselves as they interact. This could involve Kitty learning more about her place in the world outside of the X - Men, and the oc learning about their own abilities or purpose while being around Kitty.
One plot idea could be that they discover they are pregnant and then have to figure out how to break the news to their superhero friends. They might be worried about how it will affect their team dynamics.
The character interactions are really engaging. For example, Naruto's brash and determined nature contrasted with Kitty Pryde's more reserved and intelligent personality can lead to some really interesting dialogues and plot developments. Also, the fanfiction can explore how their powers might interact or complement each other, like Naruto's ability to use shadow clones and Kitty Pryde's phasing ability.
One common theme is friendship development. Since the OC is new in the Marvel world, often the story focuses on how they become friends with Kitty Pryde. Another theme is power exploration. The OC usually has a unique power, and the fanfiction may explore how that power interacts with Kitty Pryde's phasing ability. For example, they might have to work together to defeat a villain who is immune to one of their powers but vulnerable to the combination of both.
One interesting fanfiction could be where Wolverine takes Kitty Pryde on a special training mission in the Canadian wilderness. It would be a great chance to explore their mentor - mentee relationship further, and also show Kitty Pryde learning some of Wolverine's more brutal combat techniques in a secluded and challenging environment.
Their powers. Kitty can phase through solid objects and Rogue can absorb powers and memories of others. These powers create a lot of interesting scenarios in fanfiction. For instance, how would Rogue react if she accidentally absorbed Kitty while she was phasing? It's a unique dynamic that fanfiction writers can explore.
You can start by having them meet in an unexpected situation. For example, the OC could be in trouble and Kitty Pryde comes to their rescue. This creates an initial connection. Then, give them common goals. If they both want to stop a certain villain, they'll have to work together and that will bring them closer.