(This is for the fanfiction "Crossover Together". Info may change from canon information)
Hiromi Shiota is Nagisa Shiota's mother.
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, Nagisa. In the anime, her hair is shown as dark navy blue, implying Nagisa inherited his blue hair from her.
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. Later though, she becomes more lenient with Nagisa especially after her encounter with Akira Takaoka. Since then, the two appear to be on better terms.
Much of her youth wasn't really as successful as she liked: she grew up with parents who made her focus on studies instead of being herself. She had failed in enrolling in Keisetsu University, and when old enough for a job, failed to be hired in Hishimaru - a movie company. This incident in particular nearly made her kill the director, and she was charged with a 5,000 yen for attempted murder, as her outburst caused the director to be put in medical care for a few days.
When she gave birth to Nagisa, she tried to emulate her own life onto him. This goal of hers soon became an obsession, and she took full control over Nagisa's life: making him into the girl she always wanted herself to be, and forcing the life goals she couldn't accomplish onto him instead. She forced Nagisa into attending an all-girls school, where he first met Yugure Kagayaki. Her forcing and controlling nature got to the point when her husband left her, and Nagisa Shiota running away, leaving her all alone.
When she went to Tokyo to find Nagisa, she ran into Aladdin over in the market, and as such followed him back to Nagisa's apartment and finally reuniting with her child. Hiromi briefly caught up with him; asking if he entered Keisetsu university, only to find he enrolled in Orora High School instead. She at first disapproved, but became more acceptable of it when she heard Nagisa was in top class, and said he could end up in Hishimaru if he kept up the good work. When the two had a moment alone, she stated that Orora High was not good enough for him, and suggested a school transfer. Nagisa tried to protest, but Hiromi quickly lashed out at him: mauling him into apologizing for "being selfish".
The next day she had Nagisa dressed as a girl, and made him go to school that way for one day before meeting with Gakuho Asano for the transfer. While Hiromi was fine with it, when asked of Nagisa's opinion, she told him that it's the parents' job to decide their children's future, and to not worry about it. This made Gakuho decline her, and she stormed out in a huff. That night, Hiromi made dinner for Nagisa and herself, planning to actually poison him and take him away, but Nagisa foresaw this and left her again. She chased after Nagisa until she got to Orora High School, meeting up with Nagisa on the rooftop. She berated him for running away on her again, and when he finally stood up to her, she attacked him, punching him senseless and almost killing him before Undertaker and Aladdin arrived. Aladdin pleaded for her to stop, making her try to attack him instead just for Nagisa to strike her to the ground. She ordered Nagisa one more time to go home, but when he refused, she left him.
Hiromi stayed at Nagisa's home for the next few days, her presence keeping Nagisa from coming home. The encounter on the roof left her questioning herself, and after eavesdropping on Kyoya Ootori's meeting, jotted his behavior as nothing but acting for Hishimaru, and thus placing herself in denial. Overtime, she started to doubt it all, and one night eventually left the apartment. She was found and captured by Akira Tataoka to be used as bait, and once Nagisa and Aladdin came out, Tataoka ordered her to kill Aladdin so she could live. Seeing her son close to dying, she lashed out at Tataoka, and in the flight gouged his eyes with her own hands. However, Tataoka grabbed her head, and slammed it into the ground, knocking her out.
The attack resulted in her being put in emergency care for the next two weeks, her skull suffering a fracture and tearing multiple muscles. While there, she finally admitted to her faults, and deeply apologized to Nagisa for all the trouble she'd put him through, seeing well how much better he was without her involvement. By the end of the series, she's seen with her ex-husband, now back together, much to Nagisa's joy.