One idea could be a story where they have to work together on a secret mission outside of their normal school duties. They discover new sides of each other during this adventure.
Maybe a plot where they both get trapped in an alternate dimension and have to rely on each other's skills to get back. Koro - sensei's unique abilities and Karasuma's combat and strategic skills would make for an exciting combination. For example, Koro - sensei could use his speed and shape - shifting to find a way out, while Karasuma figures out the logic behind the dimension's rules.
They could start by having more conversations outside of work - related topics. This would allow them to bond on a personal level. For example, they could talk about their hobbies or past experiences. Karasuma might share his military training stories, and Koro - sensei could talk about his travels before coming to the school. As they get to know each other better, their relationship would develop into a more complex and interesting one.
Another plot could involve a lemon - growing competition among the students, and Koro Sensei serves as the judge. He gives out his unique rewards and punishments based on how well the students grow their lemons. Along the way, there are funny mishaps and heartwarming moments as the students learn about gardening and competition.
One interesting 'human Koro Sensei fanfiction' could be about Koro Sensei living a normal human life. He might be a teacher in a regular school, facing normal teaching challenges like dealing with difficult students or strict school regulations. For example, he could use his unique teaching methods to inspire a group of underachieving students to strive for better grades.
There could be a fanfiction where Koro Sensei in human form has to deal with his students in a completely different setting. For example, instead of teaching in a classroom, they are all on a survival adventure together. He uses his unique skills and knowledge, which he had even as a human, to protect and guide the students. It could explore his relationships with the students on a deeper level outside of the typical school environment.
One great koro sensei x aguri fanfiction might be the one where they share a quiet moment under the cherry blossoms. It beautifully captures their unique relationship.
In some koro sensei fan fiction, there are alternate timelines. For instance, in one timeline, Koro - sensei might not have been the target of assassination and instead becomes a full - time regular teacher at Kunugigaoka. This changes the dynamics of the entire story. The students grow in different ways, and there are new story arcs that revolve around the students' academic and personal development without the threat of their teacher's impending doom.
Maybe in the 'koro sensei turns human fanfiction', he has to deal with his past as an assassin. As a human, he might have flashbacks of his former life and try to atone for his sins. He could start by teaching self - defense or martial arts to kids in a local community center. And he might also face danger from his former assassin comrades who don't like the idea of him becoming a 'good' human.
One plot idea could be that Keita struggles in a particular subject at school and Sensei offers him extra tutoring. During these tutoring sessions, they gradually develop a deeper understanding of each other and form a unique bond. This could lead to some comical moments as Keita's sisters might get jealous of the time he spends with Sensei.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of various fanfictions, and you're likely to find some good koro sensei x aguri ones there.
One idea could be Naruto being trained by Kakashi's father, Sakumo. Since Sakumo was known for his skills, he could teach Naruto some unique jutsu and a different perspective on being a ninja. Another plot could involve Naruto being mentored by Tsunade's younger brother Nawaki. It would change Naruto's development as Nawaki might have his own special way of teaching. Maybe he'd focus more on medical ninjutsu combined with combat skills.