One idea could be a sports competition at the high school where Naruto and his friends compete in a ninja - themed track and field event. Another could be a school dance where there are some unexpected alliances and rivalries revealed. Maybe a new student arrives who has a mysterious past related to the shinobi world.
One plot idea could be that Naruto is summoned to the High School DxD world by a powerful magic user who mistakes him for a powerful demon. Once there, Naruto has to prove that he is not a threat while also trying to find a way back home. Along the way, he befriends some of the students at the school and helps them with their own problems, like protecting the school from a sudden attack by a group of rogue devils.
A plot idea could be that some of the devils in High School DxD want to learn the secrets of chakra from Naruto. So they kidnap him to their world. Naruto then has to find a way to escape while also dealing with the political intrigue among the devils, angels, and fallen angels. Another idea is that Naruto's shadow clones could be mistaken for some new type of summoned creatures in the DxD world.
A possible plot for 'naruto high school harem fanfiction' could be that Naruto is given a special project in high school where he has to work with a group of girls. As they work together, the girls start to develop feelings for Naruto. There could be drama within the group as some girls are more forward in their feelings while others are shy. And Naruto, being his oblivious self at first, slowly starts to realize the situation and has to figure out how to handle all these new emotions and relationships.
Well, in high school Naruto fanfiction, a cool concept could be Naruto forming a ninja club at school. They train after school hours and enter into friendly competitions with other clubs. Or perhaps a story where Naruto discovers a hidden ninja heritage in his high school, like an old dojo or a secret scroll left by a former ninja. Also, a high school where the characters are all descendants of Naruto - era ninjas and they have to live up to their ancestors' legacies while dealing with normal high school stuff like exams and prom.
Well, a great plot might be that Ino is tutoring Naruto in a difficult subject like chemistry. As they study together, they start to develop feelings for each other. Also, there could be a high school play where Naruto and Ino both audition for the lead roles. There's a lot of drama and competition, but in the process, they fall for each other. And perhaps there's a mystery in the school, like something going missing from the art room, and Naruto and Ino team up to solve it, bringing them closer.
Well, it could be that Fem Naruto is a transfer student to Konoha High School. She tries to fit in but finds it difficult as she has a different style of ninja - skills compared to the local students. As she tries to adapt, she also uncovers a plot by a group of students who are trying to undermine the school's headmaster. With her determination and unique skills, she sets out to stop them and in the process, earns the respect of her classmates.
One idea could be that Naruto and Sakura are paired up for a school project. Along the way, they start to discover new sides of each other. Maybe Naruto shows his hidden intelligence and Sakura her more vulnerable side. This could lead to a budding romance as they spend more time together outside of their normal friend group at school.
One idea could be that Naruto and Gaara are paired for a school project. Naruto's outgoing nature clashes with Gaara's more reserved one at first, but as they work together, they discover they have more in common than they thought, like their love for their families. They end up becoming good friends and helping each other through high school challenges.
One plot idea could be that Kiba and Naruto are paired up for a school project. They start off bickering but gradually realize they have a lot in common and form a strong friendship that might turn into something more. For example, they discover their shared love for adventure while exploring an old abandoned part of the school for their project.
One interesting plot idea could be Naruto and Fem Sasuke being paired up for a school project. As they work together, they start to see each other in a new light. Naruto realizes Fem Sasuke is not as cold as she seems, and Fem Sasuke sees Naruto's determination and kindness. This could lead to a budding friendship or even a romantic relationship.