One possibility could be a crossover universe where Naruto somehow ends up in the Sekirei world. The kiss between Naruto and Miya might be a result of a misunderstanding at first. Maybe Naruto mistakes Miya for someone from his own world and in a moment of confusion, there's a kiss. Then, it could lead to a whole adventure as they try to figure out how to get Naruto back to his own world while also dealing with the Sekirei rules and the reactions of other characters in the Sekirei world.
First, you need to establish the characters well. Since it's a crossover, make sure to describe how Naruto and Miya are in this new context. For the kiss scene, build up the tension before it. Maybe have them have a deep conversation where they realize they have a connection. Then, for the actual kiss, describe the emotions and sensations in detail. After that, introduce conflict. Maybe some of the other Sekirei are jealous or there are rules against their relationship. Keep the story flowing with action and more character development.
A minato x miya sekirei fanfic can take many forms. It might be a romantic exploration of their relationship, with tender moments and deep conversations. For example, the author could write about a time when Minato confesses his feelings to Miya and how she responds. Or it could be more action - oriented, with the two of them teaming up to fight against a common enemy in the Sekirei world. The fanfic might also introduce new elements to the Sekirei lore, like a new type of Sekirei that they have to deal with together.
You can start by looking on popular fanfic websites like FanFiction.net or Archive of Our Own. Just search for'minato x miya sekirei' and you'll likely find a variety of fics to choose from.
A possible plot is that there's a new threat that combines the dark forces from Naruto, like the Akatsuki, and the antagonists in Sekirei. Naruto and Miya Sekirei have to put aside their differences and work together. Maybe they start by sharing their respective combat techniques. Naruto could teach the Sekirei about chakra control, while the Sekirei could show Naruto some of their unique powers that could be useful in combat against this new threat.
One possible plot could be that Naruto somehow gets involved in the Sekirei Plan while still having the power of the Juubi within him. He might use his ninja skills and the Juubi's power to protect the Sekirei from those who would use them for evil purposes. For example, he could face off against Minaka Hiroto, the creator of the Sekirei Plan, if he discovers that the plan is causing harm to the Sekirei. Naruto's values of friendship and protecting the weak would likely drive his actions in this fanfic scenario.
Perhaps the OC is a scientist who has been researching a new form of energy. This energy is actually what powers the Sekirei. The OC's research attracts the attention of a group of Sekirei. One Sekirei in particular befriends the OC to learn more about this energy. As they spend time together, the OC begins to understand the Sekirei's world better and helps them find a way to break free from the constraints of the Sekirei Plan.
In this type of fanfiction, it could be that Naruto enters the Sekirei world during one of his training missions gone wrong. He is neglected by the Ashikabi (the Sekirei masters) at first because he doesn't seem to have any Sekirei - like powers. However, Naruto's strong will and determination attract a Sekirei who is also different from the others. They start to train together, Naruto teaching the Sekirei about ninja values like loyalty and perseverance. As they progress, they start to change the perception of what it means to be strong in the Sekirei world, and Naruto becomes an important figure despite the initial neglect.
Well, it could be that in this fanfiction, Naruto is given a mission that goes against the interests of the Sekirei. He might have to choose between his loyalty to his original world and the new relationships he has formed with the Sekirei. If he chooses his old world, the Sekirei could see it as a betrayal.
Well, in a Naruto and Akame kiss fanfic, it might start with Akame being sent on a mission to Naruto's world. She's initially confused but Naruto helps her. They train together and learn from each other's fighting styles. As they spend more time together, feelings develop. The kiss could be a moment of realization for both of them that their feelings are more than just friendship, like a climax of all the shared experiences they've had.
One possible plot could be that Naruto and Ino are on a mission together. They face a dangerous situation where they have to rely on each other completely. In the heat of the moment, after they survive, they share a passionate kiss as they realize how much they mean to each other.