Well, a great storyline might involve Fem Naruto being mistaken for a new type of devil or some sort of mysterious being in the Highschool DxD world. As she tries to clear up the misunderstanding, she gets drawn into the complex politics between the different factions. She could also have a rivalry with some of the more powerful female characters in the DxD world, like Rias, which would lead to some intense and exciting battles.
One interesting storyline could be Fem Naruto joining the Occult Research Club in the Highschool DxD universe. She could use her ninja skills, like her shadow clone jutsu, in unique ways during club activities or battles against devils and fallen angels. Another could be her forming an unexpected friendship with Issei, perhaps teaching him some ninja stealth techniques which come in handy during his escapades.
A possible storyline is that Fem Naruto has a special power that is coveted by the various groups in Highschool DxD. This power could be related to her chakra, which is something entirely new in that world. As she tries to protect her power and herself, she teams up with some unlikely allies from the DxD universe. Maybe she uses her Naruto - like determination to inspire those around her, including some of the more jaded characters in the DxD world, to fight for what's right.
Another storyline could involve Sage Naruto teaching some of the characters in Highschool DxD his ninja techniques. Imagine Naruto showing Issei how to use shadow clones to his advantage in battles or training sessions. This would not only add a new dimension to the battles in the DxD world but also create some really fun and comical moments as the characters from two different universes interact.
A fanfiction might explore a story where the Occult Research Club members are all transported to a different dimension. In this new world, they have to find a way back home while facing new enemies and challenges. Rias could use her leadership skills in a different way, and Kiba might discover new powers within himself to protect the group. This would also test the bonds between the characters in a whole new setting.
Another could be Mittelt forming an unlikely friendship with a character from a different faction in the Highschool DxD universe. For example, she befriends a member of the fallen angels' group that her side is usually at odds with. This could lead to all sorts of plot twists as they try to bridge the gap between their two groups. And it would be really cool to see how Mittelt grows and changes through this relationship.
Well, a great storyline could involve a slave character who has a unique relationship with one of the main characters from Highschool Dxd. Maybe they start off as just a slave but through shared experiences, like fighting together against a common enemy, they develop a deep bond that changes the whole dynamic of the story and challenges the traditional master - slave relationship in that world.
One interesting storyline could be about a new character who joins the school and has a unique power that changes the power dynamics among the existing groups. This new character might start as an outcast but gradually earns the respect of the others through their actions.
Another possible storyline is a love triangle between a Saitama Highschool student, a character from DxD, and another student from their own school. This would add an element of drama and emotion to the fanfiction, as they navigate their feelings while also dealing with the supernatural elements of the DxD world.
One interesting storyline could be about a new character who has a unique power that shakes up the power dynamics in the Highschool DxD world. For example, a character with the ability to nullify all magic for a short time, creating new challenges and alliances.
One interesting storyline could be about a new character in the Futa Highschool DxD universe who has unique powers and has to navigate the complex social and power dynamics. For example, they might be a half - demon, half - angel and face discrimination from both sides.
A lot of fanfictions explore Irena's relationships with the other main characters. Maybe she forms an unlikely friendship with a character who is very different from her. This can lead to some really fun and heartwarming interactions as they learn from each other and grow together.
There might be a fanfiction where Fem Issei has a special power that only she, as a female version of Issei, can possess. For example, she could have a more refined form of the Boosted Gear that is attuned to feminine energy. This could lead to new storylines and battles that deviate from the original plot. She may also form unexpected alliances with other characters based on this new power.