A third storyline could be a fusion of the two worlds. The schools in both universes combine, and the students have to learn both regular academics as well as assassination techniques. Koro - sensei could teach some classes alongside the regular teachers from KHR. This would lead to some very chaotic and interesting classroom dynamics, with students from different backgrounds and abilities trying to co - exist and learn from each other.
Another storyline could involve a character from Assassination Classroom being sent to the KHR world. Nagisa, with his assassin skills, could get involved in the mafia - like affairs of the KHR universe. He might use his stealth and combat abilities to help out the good guys in that world, or perhaps he gets caught in the middle of a power struggle between different mafia families.
One possible plot could be that the students from Assassination Classroom are sent on a mission to the world of KHR. They could end up having to help the Guardians in a battle against a new and powerful enemy. Tsuna and his friends would be initially suspicious of these strange new allies but soon realize their skills and unique abilities can be of great help.
First, understand the personalities of the characters from both KHR and Assassination Classroom. For example, Reborn from KHR is a strict and somewhat mysterious tutor, while Koro - sensei is a fun - loving but deadly octopus - teacher. When creating an interaction, think about how their different traits would clash or complement each other. Maybe Reborn would be intrigued by Koro - sensei's unique abilities and try to find a way to use them for his own training methods.
A plot could revolve around a time - travel aspect. A student accidentally travels back in time to before Koro - sensei was experimented on and tries to change the course of events. This would involve a lot of moral dilemmas as they might be changing the future for better or worse.
Definitely Nagisa. In the crossover, he could be the one who has the hardest time adapting to the new world of KHR. His assassin skills would be put to the test in a different way compared to Assassination Classroom. He might form an interesting friendship with Tsuna, as both are somewhat timid at first but have great potential within them.
One possible storyline could be that Nagisa gets fatally injured during a particularly dangerous mission against a powerful new enemy that the class wasn't fully prepared for. Another could be that he sacrifices himself to save his classmates from a deadly trap set by the anti - Earth forces.
One idea could be that the main character uses his unique skills from the Assassination Classroom to protect the girls in his harem from other threats outside of the classroom. For example, a new group of assassins comes to town and he has to keep his harem safe while also dealing with school life.
One plot idea could be Itona's struggle to fully adapt to the classroom environment. He could start off as an outsider but gradually form deep bonds with his classmates. Maybe he discovers a new hobby or talent that helps him fit in better, like joining a music club in the school within the Assassination Classroom world.
Well, you could write a fanfiction where the students develop new and unique assassination techniques. It could also be interesting to write about a time - travel plot, where a student goes back in time to change something that would affect the whole assassination classroom scenario. Or perhaps a story that focuses on the relationship between Koro - sensei and a particular student, like Nagisa, and how it develops in unexpected ways.
Sure. 'A Day in the Life of Korosensei' is a great fanfic. It shows Korosensei's daily interactions with the students in a very humorous way. Another one is 'Korosensei's Secret Mission'. It gives an interesting take on what Korosensei might be doing outside of the classroom.
Well, perhaps a group of students time travel to a future where they see the consequences of not assassinating Koro - sensei in time. This could give them new motivation and strategies when they return to their own time. Or, what if Koro - sensei time travels to different points in the students' lives and helps them in ways that are not related to assassination, like helping a student deal with a family issue in the past.