Hiromi Shiota

Hiromi Shiota is the mother of Nagisa Shiota and the ex-wife of Nagisa's Father. As of chapter 178, she is getting back together with her ex-husband to their son's joy.

Appearance
She has been described as "pretty, but strict looking." She has short dark hair and is said to hold a strong resemblance to her son. In the anime, her hair is shown as dark navy blue, implying Nagisa inherited his blue hair from her.

Personality
In the beginning, Hiromi is portrayed as antagonistic to Nagisa, being extremely controlling of Nagisa's life. She forces him to keep his hair long, and makes him wear female outfits despite his dislike of it. When defied by others, she bursts into loud fits of rage, like when she yelled angrily at Koro-sensei. Later though, she becomes more lenient with Nagisa especially when her son saved her life from an assassin hiding to attack Koro-sensei. Since then, the two appear to be on better terms.

History
Not much is known about Hiromi's past however she has revealed that her parents forced her to study often and she was never able to dress herself up. At some point, she met and married an unnamed man and she became pregnant with their child. Due to her own "controlled" childhood, Hiromi wished for a girl so that she could live the life she had wanted through her. However, she had a son, Nagisa, instead. Despite having a boy, Hiromi still tried to live the life she wanted through him. Her methods included keeping Nagisa's hair long and occasionally forcing him to crossdress. According to Nagisa, it was Hiromi's controlling and semi-psychotic temper that drove his father away.

In the few instances that Nagisa brought some of his friends (like Karma and Sugino) to his house, Hiromi adopts a civil but cold attitude, leading Sugino to think of her as strict.

Plot
Hiromi makes her debut appearance in Chapter 112. When Nagisa comes home from school, she proposes to her son to have him transferred back to the main campus based on his improving results. Nagisa initially protests at this but is immediately silenced by Hiromi's domineering look and rising temper. She explodes and starts ranting at how she is essentially burdened to look after Nagisa and force him to follow the path in later life she laid down for him. Hiromi dismisses his concerns and resolves to meet with his teacher the next day.

Hiromi arrives at the mountain classroom and meets Nagisa's teacher, unaware that Korosensei is awkwardly disguised as Karasuma. Hiromi demands that Nagisa be reinstated back to his former class. When Korosensei asks how Nagisa feels about this, Hiromi forces her son to be silent and states that it is for the parent to decided for their child's best interests. Korosensei then understands why Nagisa is the person he is now and refuses to comply, taking his wig off in dramatic fashion and shocking Hiromi. He cites Hiromi's inferiority complex in ordering her son into submission and not allowing Nagisa to truly express himself. In a fit of rage, Hiromi storms out of the classroom.

That night Hiromi drugs Nagisa during dinner and takes him back to the mountain classroom. When he awakes, she orders him to burn down the classroom and afterwards make him beg to the principal to let him return to the main campus. Nagisa refuses but their argument is cut short by a hidden hit man who got annoyed at the loud noise. Fearing her life, Hiromi is frightened but witnesses Nagisa defeat the assassin. She falls unconscious with the last words hearing her son will leave her. The next morning she wakes up to find Nagisa cooking breakfast. He states that he'll relieve some of his mother's burden and do house chores but requests that he be allowed to stay with Class 3-E. Hiromi begrudgingly agrees.

Her next appearance is after the school festival. She arrives too late to try out Class 3-E's acorn noodles (which had run out due to the unexpectedly high demand following a positive critical review) but is given one of the last drinks by Nagisa. Mother and son discuss the latter's well-being since that night, and she sees how happy Nagisa is with Class 3-E. To that end she allows him to stay with the class but makes him promise not to stop living her until he graduates from high school. She leaves in good spirits but not before telling the real Karasuma that she will keep his secret about being bold, prompting Karasuma to hunt down Korosensei.

Hiromi makes another appearance in Chapter 167. By then, March had arrived, the national secret about Korosensei and Class 3-E has become public knowledge and Korosensei is trapped. On the night of the deadline, Hiromi catches Nagisa at home preparing for the battle to come, now really knowing why Nagisa had been so assertive throughout the year. Initially scared, Nagisa is allowed by his mother to go on ahead but she warns him not to be reckless. Happy at finally being understood and accepted, Nagisa departs by jumping off the balcony, prompting a startled Hiromi to wonder what constitutes as being reckless.

Hiromi, along with Nagisa's father, reappear in chapter 178 as attendants to their son's junior high graduation. Mr. Shiota reveals Korosensei visited him a month ago and told him of Nagisa's wish that his parents would get back together. They then reveal they are getting back together, much to Nagisa's joy.

Abilities
Hiromi has not displayed any unique abilities.

Nagisa Shiota
Nagisa is Hiromi's son and only child. She originally wanted a girl and continually told him that. At first, their relationship seems to be that of a prisoner and a warden with Hiromi ordering Nagisa to be quiet and him  obliging. Hiromi has been shown to verbally (possibly even mentally and physically) abuse Nagisa, screaming at him when he tried to defy her and harshly yanking out his pigtails. However, ever since he saved her from an assassin going after Korosensei, Hiromi seems to have changed her ways and has begun building a good relationship with her son.

It is because of Hiromi's complex temperament that Nagisa is able to discern another person's emotions by reading their faces, thus building the fundamentals for him to be talented as a potential assassin.

Nagisa's Father
Although the two weren't originally shown interacting with each other, it is known that he feels guilty for "walking out" on his wife and son. According to Nagisa, it was Hiromi's controlling nature that drove him away. It is unknown if they are divorced or just separated but it can be assumed that they are no longer married. However, as of chapter 178, they are giving it another try much to Nagisa's happiness.

Trivia

 * Revealed by Korosensei in a flashback, "Shiota" seems to be Hiromi's maiden name rather than her married name. This is also why Nagisa was one of the few characters to be known by their first name as he wanted to make the transition back to his "old name" easier in the event his parents got back together.