Hidden Soul ~ The Nagisa Shiota Fanlisting

Nagisa is the son of Hiromi Shiota and her (presumably ex) husband. His mother had hoped for a daughter so she could experience all the things she had missed as a child through her, but got a son instead. As a result, she dictated his life from forcing him to keep his hair long, to being forced to crossdress and verbally abused him whenever he spoke against her. Her personality also caused her husband to leave her and Nagisa.

He was revealed to formally have been in Class D during his first two years of middle school before falling into Class E due to poor grades. During those two years he hung out with fellow classmate Karma Akabane though they slowly drifted apart. Soon after starting the new term as a Class E student, Nagisa met Kaede Kayano. She gave him what would become his signature pigtails instead of the ponytail he usually uses to keep his long hair from being less noticeable, thus beginning their friendship.

As the narrator and main protagonist of the series, Nagisa is the student that is given the most screen time out of all his classmates. Introduced in Chapter 1, after homeroom is started by Korosensei, Nagisa gives the command for the class to stand. They all draw their guns, aim and fire at Korosensei while he takes the register. Nagisa listens to the creature lecture the class on their supposedly simplistic plan and demonstrates the effect the special bullets have on him if hit, much to Nagisa's astonishment. Nagisa, along with the rest of class 3-E tidy up the classroom under Korosensei's instructions.

When Kaede Kayano whispers to him pointing out the permanent crescent moon in the sky, Nagisa remembers the destruction of the moon and the meeting and introduction of the culprit. This happened along with Karasuma from the Ministry of Defense both explaining and actively showing what their future jobs will be, along with revealing the 10 billion yen reward.

Later, while thinking about how the students of Class E are not normal students, Terasaka, Yoshida and Muramatsu approach him about working on an assassination plan, which he agrees to do with them. When Korosensei is seemingly less alert Nagisa attempts to strike him with an anti-sensei knife. Korosensei dodges it but it turns out to be a feint as Nagisa throws himself onto his teacher with a grenade around his neck. Terasaka detonates it via remote and the plan seems to have succeeded. However Nagisa had been covered by Korosensei's shedded skin while the target escaped the blast. Initially extremely angry that Terasaka and his friends had pulled such a stunt and not caring about their classmate's welfare, Korosensei nevertheless praises how Nagisa had approached him in such an innocent manner but hiding his real motives.

From Wikia (read more?)