The special aspect of Isogai fanfic in Assassination Classroom is the new scenarios it creates. In the anime and manga, we see Isogai in a set of given situations. But in fanfics, he could be put in entirely different adventures. He might be the key to solving a mystery that the whole class gets involved in. Or he could have a special power or ability that was never shown in the original, which would lead to a whole new set of challenges and growth for his character.
One thing that makes Isogai fanfic in Assassination Classroom special is the exploration of his character. In the original, Isogai is a hard - working and responsible student. Fanfics might expand on his backstory, like his family life. For example, a fanfic could delve into how his family's financial situation affects his dreams and actions at school. Also, fanfics often explore his relationships in more depth. His friendships with other classmates could be developed further, showing different sides of his loyalty and kindness.