AKABANE KARMA

He is one of Nagisa's closest friends and considered to be the strongest and smartest amongst the class 3-E students. He is the first one to be able to inflict injuries on Korosensei during their first meeting. He was suspended from school prior to Korosensei's arrival as the class' homeroom teacher due to his mischievous behaviour. Unlike most students in the class that were relegated there due to their low grades, Karma is one of the school's most gifted students, but developed a rebellious attitude due to his previous teacher's betrayal after he severely wounded a top third-year student while saving a bullied student from class 3-E, as despite believing he has done the right thing, his teacher revealed that he was only siding with him due to his grades to increase his reputation and did not want to be held responsible for what happened, Karma then proceeded brutally beat the teacher. Because of this experience, Karma at first distrusted Korosensei, but he is shown that he is unlike the other treacherous teachers at the school, making him slowly accepting him.

Information Source: Wikipedia