Well, you could write a fanfiction about Naruko's arrival in the DxD world and how she adjusts to the different culture and rules there. It could be really fun to see her reactions to things like the Rating Games or the different devil clans. Or perhaps a story where Naruko tries to teach some of her ninja techniques to the DxD characters, and they in turn teach her some of their magic.
A great idea for Naruko DxD fanfiction would be a time - travel story. Naruko somehow gets sent back in time in the DxD world and has to prevent a major catastrophe from happening. This would involve her using her wits and skills, and also interacting with younger versions of the DxD characters. It could add a whole new layer of drama and adventure to the fanfiction.
One idea could be a new character arrives at the school who has a unique power that disrupts the existing power balance among the student groups. Another could be a time - travel plot where a character goes back in time to change an important event in the Highschool DxD universe. Maybe a crossover with another popular anime, where characters from both shows interact in the Naruko Highschool DxD setting.
One idea could be a story where Naruto and Naruko train together in a new and secret jutsu. They face various challenges during the training and in the process, they learn more about each other's strengths and weaknesses.
A crossover with a fairy - tale world could also be great. Picture Naruko in a world full of talking animals and enchanted forests. She could have adventures, help the fairy - tale characters solve their problems, and at the same time, learn about different forms of magic and kindness that are prevalent in that world.
Well, a possible plot for Naruko and Kyuubi fanfiction is that the Kyuubi's power starts to merge with Naruko in a way that gives her new and unexpected abilities. She could then use these abilities to change the way the ninja world views her. Maybe she becomes a symbol of hope for those with tailed beasts within them. Another plot could be that Naruko has to enter the Kyuubi's mindscape to help it heal from some old wounds. In doing so, she learns about the Kyuubi's past and how it came to be so feared. And finally, they could go on a journey together to find a lost artifact that has the power to either free the Kyuubi completely or bind it more tightly to Naruko, depending on how they choose to use it.
Another aspect could be the family dynamic. If they are mates, they would likely start a family. How they raise their children to be strong yet kind ninjas, passing on the values of their respective clans, like Naruto's Uzumaki spirit and Naruko's (assuming a female version of Naruto) own unique traits.
One plot idea could be Naruko and Sakura going on a mission together in a new and dangerous area, and they have to rely on each other's unique skills to survive. Another could be them having to deal with a misunderstanding within the village that threatens their friendship.
One idea could be to explore new alliances within the DxD universe. For example, a character from a minor faction teams up with the main characters to achieve a common goal in the conquest. Another could be to focus on a character's personal journey of power - up during the conquest, like how they train and overcome their weaknesses.
One idea could be to focus on the characters' relationships outside of the main plot. For example, how the students interact during normal school days, like study groups or after - school clubs. Another idea is to create an alternate universe where the rules of the dxd world are slightly different in the high school setting, which could lead to new adventures and challenges for the characters.
One idea could be exploring the main character's journey in the gaming world within the DxD universe in a more in - depth way. For example, how they level up their skills not just in combat but also in strategic thinking and relationship - building.
One idea could be to create a story where the Akatsuki members from Naruto end up in the DxD universe and have to deal with the devils, angels and fallen angels. They might use their unique ninja skills in battles against the supernatural beings in DxD.