Born with a weak constitution, Hiromi desperately wished to conceive a child with Kurama, but their attempts failed to produce a child, even resulted in a miscarriage, and her health deteriorated from the effort. Their last resort was in-vitro fertilization , and this time, they were lucky. The resulting child was Mariko, but Mariko's DicloniusSilpelit nature, caused by Kurama's exposure to an escaping Diclonius child, was unknown to both her parents. This lack of knowledge was due to Hiromi believing it was more fun to wait and see the child's sex at birth instead of having an ultrasound scan during her pregnancy. During Mariko's birth, there was a complication wherein the doctors discovered Hiromi had cervical cancer, so doctors undertook the removal of her entire uterus at the same time Mariko was delivered via Caesarean Section. This operation would make Mariko her only daughter.
Hiromi dearly loved Mariko as soon as she saw her, but her husband was shocked and distressed at the sight of the newborn, knowing many Diclonius children are the primary cause of death for their families once the children's vectors develop at age three. Hiromi had no idea that his job, kept secret from her, was to euthanize infant Diclonii as soon as they were born. He immediately began to strangle Mariko, but Hiromi, shocked to see this and weakened by the surgery removed during birth stopped him before collapsing. When he tried again later, a tearful Hiromi, beset by massive internal bleeding, rose from her hospital bed to beg him to stop and make him promise to love their child and not kill her. She then collapsed and bled to death, dying in Kurama's arms as he begged her to wake up.
After her death, Kurama held to his promise to Hiromi, albeit with mixed results. To those who would ask, he would respond about his family to say his family was dead, even going so far as to say he killed both his wife and his daughter. In his eyes, this was indeed the truth. Kurama later sees Hiromi in visions of her and Mariko walking into heaven together.
In the anime, Kurama sees visions of Hiromi just before he dies alongside Mariko, imagining a life with his wife and daughter they could have had if Mariko hadn't been born with horns.
Hiromi shares her voice actress with her daughter in the English dub: Luci Christian.
It seems unlikely that Nana ever knew of Hiromi; had she, she most likely would have imprinted on the idea of her being her mother.
How much did Hiromi know/realize about her husband's work?