One idea could be Ravel's adventures in the school's magic club. She could be working on new spells and facing challenges like accidental magic mishaps. For example, she might try to create a spell to make plants grow faster for a school project, but instead makes them grow out of control and has to figure out how to reverse it.
A plot could also focus on Ravel's growth as a character. She could be facing self - doubt about her abilities compared to others in the school. She then decides to train extra hard in a particular area, like combat magic. Along the way, she meets a mentor who helps her realize that her unique skills are valuable in their own way and she gains more confidence.
One idea could be a sports competition between the Naruto characters and the Highschool DxD characters. They could compete in something like a ninja - themed obstacle course that combines elements from both universes.
One idea could be that Naruto, through some sort of interdimensional rift, ends up in the world of Highschool DxD. Ravel could be intrigued by this strange new being with his unique powers. Maybe Naruto has to team up with Ravel to face a common enemy in the DxD world, like a rogue group of devils. His ninja skills would be a novelty there and could help them in battles.
Growth and self - discovery are also prevalent. Ravel might be trying to figure out what she really wants to do in the future, whether it's a certain type of magic she wants to master or a career path she's interested in. She could explore different areas of study or magic types and in the process learn more about herself.
A more complex plot could be centered around a prophecy that foretells the destruction of the Highschool DxD world. The characters then have to embark on a journey to find the source of this prophecy and try to prevent it. Along the way, they discover secrets about their own powers and the true nature of the different factions, and have to make difficult choices that could either save or doom their world.
A third plot idea might be Sona trying to modernize the traditions of the devil world within the context of the school. She could face opposition from more conservative devils, and the story could explore her struggle to bring about change while still maintaining her position and respect.
One idea could be a new character who is a killer but has a hidden noble purpose. Maybe they are targeting rogue devils that are harming humans secretly. This would add an element of mystery and action to the fanfiction.
Maybe Jesus could have a special mission in the Highschool DxD universe. For example, he might be there to stop a great evil that is brewing and uses his powers in a way that is different from the traditional powers in the series. He could team up with Issei and the others, bringing a new dynamic to their group.
One interesting plot idea could be Murayama discovers a hidden power within herself. Maybe she has a connection to an ancient artifact in the Highschool DxD universe that gives her unique abilities, like the power to control time briefly. This could lead to her having to protect this secret from both the devils and the angels in the story.
A possible plot is that a group of students in High School DxD start a gaming club, but they accidentally discover that the games they play are linked to some ancient and powerful magic. As they delve deeper into these games, they uncover secrets about their world and have to face off against enemies who want to use this magic for evil purposes.
One idea could be a new character who is a futa and has unique powers related to both male and female aspects. They could join the Gremory group and cause some interesting dynamics, like having a different approach to battles and relationships within the group.