Nagisa Shiota is the main protagonist in the anime Assassination Classroom.
Nagisa is a high school student to Koro Sensei at Kunugigaoka Junior High School. There, he goes through the difficulty of climbing up a school hierarchy system while practicing the art of assassination. He’s gifted in the power of stealth and hand to hand combat. Unlike his classmates, he is often mistaken for a girl due to his physical appearance. His mother dislikes the fact that Nagisa is her son, desiring a daughter instead. This leads to a complicated household where Nagisa is abused by his mother.
Nagisa has four different hair styles. The first being loose, with his hair reaching his shoulders. His second hair style is a long ponytail. His last hairstyle is the most notable and used thought the anime, pigtails. The style was chosen by one of his classmates and the hair style stuck to him ever since. The final hairstyle Nagisa shows is in a timeskip seven years after highschool. His hair has been cut short, giving him a more boyish look.
Reason For Cross-Dressing
Nagisa does not crossdress out of his own volition but because of others. He is usually hasty and has a disliking for cross dressing, but if it’s for the greater good for the people around him, he will do so. He is known for his androgynous appearance, in which gets poked fun of, mainly by Rio Nakumura and Karma Akabane. Nagisa finally crossdresses in Chapter 66. He does so to go unnoticed during an assassination at a bar that his group had to pass through. He also dresses up as a girl a few more times as the series goes on, mostly against his will. This gag had stopped as of Chapter 116, when Nakamura discovered the reason why he keeps his hair the way it is, due to his mother's oppression.
Apparently, his mother always had wanted a female child since her parents never let her live her teenage years as a normal girl. She pressed her dreams to Nagisa believing that it was the best for him, usually shouting at him constantly when he said no.
She later stopped shouting at him when he showed his killer skills and protected her, thus making her return to a gentle kind behaviour towards him. This causes his mother and father to get back together.