Karma could also be the main character. He's known for his devious and intelligent nature. If he time - travels, he might use his wits to manipulate events in different time periods. For example, he could go back to the start of the school year and set up more elaborate assassination plans from the very beginning, or he could travel to a future where Koro - sensei has been assassinated and bring back some crucial information.
It could be Nagisa. Since he is one of the central characters in the original series, he would make a great time - traveling protagonist. He could travel back in time to gain more skills or knowledge to better assassinate Koro - sensei, or he might go forward in time to see the consequences of their actions in the classroom.
There's also the possibility of a new character being the main character. This character could be a time - traveler from a different dimension or future era. They could enter the Assassination Classroom world with the goal of either saving or destroying Koro - sensei, and their actions would drive the plot forward as they interact with the existing characters and the strange world of the classroom.
One possible plot could be a student from the future traveling back to the time of the Assassination Classroom. They might use their knowledge of the future events in the classroom to change certain outcomes. For example, they could try to prevent some of the students from getting into dangerous situations during their attempts to assassinate Koro - sensei.
Koro - sensei could be a likely candidate. Since he has advanced abilities, he might be able to figure out time travel in some way. He could use it to try to change his own past or to better prepare the students for their future.
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.
First, give your male OC a clear backstory. For instance, if he has a tragic past, like losing his family to an assassin, it can explain his motivation to be in the assassination classroom. Second, define his unique skills. It could be something physical like superhuman speed or a mental ability like mind - reading. This will make him stand out among the other characters.
For Karma, he might start to show a more vulnerable side in the fanfiction. Usually, he's very confident and a bit of a troublemaker. But when it comes to Rio, he could become more hesitant and self - conscious, as he starts to really care about what she thinks of him.
One possible fanfiction could be about female Karma's journey in the Assassination Classroom. Maybe she uses her intelligence and unique skills to outwit the other students in various assassination attempts. For example, she could come up with creative plans to get close to Koro - sensei while still maintaining her cool and mysterious demeanor.
One characteristic is the exploration of the unique characters. Fanfictions often dig deeper into the backstories and personalities of the students and the teacher in 'Assassination Classroom'. For example, they might expand on how Nagisa came to be so calm and observant. Another aspect is the different plot twists. Some fanfictions create alternate scenarios where the assassination attempts take on new forms or have different outcomes.
One possible fanfiction could be about Nagisa, as a girl, having to deal with the unique challenges in the Assassination Classroom. Maybe she uses her newfound femininity to her advantage in different assassination attempts. For example, she could play on the stereotypes that others might have of a girl being less of a threat, only to surprise her opponents.
One of the main themes is growth. The students in the story experience significant personal growth throughout their time with the teacher. Another theme is the value of education, as the 'assassination' lessons are also a form of unique education. And there is also the theme of friendship that develops among the students as they face challenges together.
First, think about their backstory. Where did they come from? Were they bullied in their previous school? Or did they have a family tragedy that led them to Class 3 - E? This will shape their personality. For example, if they were bullied, they might be more reserved but also determined to prove themselves. Second, give them unique skills or talents. It doesn't have to be combat - related. It could be something like being really good at cooking, which can be used in a creative way in the story. Third, consider their relationships with other characters. Do they admire Nagisa? Or do they have a friendly rivalry with Karma?