Irina Jelavić could be another possibility. As a professional assassin, she might have access to some secret technologies or knowledge that could be related to time travel. She could use it either to complete her mission of assassinating Koro - sensei more effectively or to save the students from a bad future she has foreseen.
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.
Lelouch would be a likely candidate. He has a strong sense of justice and a desire to change the world. Given his intelligence and strategic mind, if he were to discover the means of time travel, he would likely use it to correct the many wrongs in the Code Geass world, such as the oppression of Britannia. He could go back in time to prevent his mother's death and change the course of his own life and the fate of the world.
Ciel is a likely candidate. Given his intelligence and determination to avenge his family and protect his future, he might see time travel as a means to change certain events in the past. He could use it to find out more about the people who wronged his family and stop them before they act.
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.
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.
Batman himself is a likely candidate. Given his intelligence and determination, he might stumble upon a time - traveling device or technology while investigating some strange phenomenon. He would be driven by his need to protect Gotham, perhaps by preventing a future catastrophe that he has foreseen.
Star - Lord is a likely candidate. He's always been a bit of a risk - taker and his curiosity might lead him to experiment with time travel technology.
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.
Itona in the Assassination Classroom fanfic is often depicted as a complex character. He has his own unique backstory and growth arc. His relationship with other characters, like Nagisa and Karma, can be explored in different ways in fanfics. Sometimes he is shown as a more vulnerable side, which is different from his tough exterior in the original anime.
Karasuma in fanfic can be seen in various relationships. For example, his relationship with the other teachers and how they collaborate to handle the students. His interactions with the students also show his growth as a character. Sometimes, fanfic writers explore his past, which may not be fully revealed in the original work, adding more depth to his character.
In fanfic, Karasuma can be a source of stability for the students. He is not only teaching them assassination techniques but also life lessons. His no - nonsense attitude can be a guiding force for the students, especially when they are faced with moral dilemmas in their training. For instance, when a student has to decide between a quick kill and a more humane approach, Karasuma's influence might come into play.