Ryoko is the birth mother of Soichiro Arima.
Before meeting Reiji Arima, Ryoko suffered during her junior year of middle school when her stepfather sexually abused her. Ryoko mentioned this to her mother, but unfortunately her mother wouldn't believe her and blame her for her husband's reason in cheating on her. Ryoko, in a fragile state of mind would become emotionally unstable and become dangerous among her peers, it was even mentioned she was much more abusive than her Gang Leader boyfriend.
Upon meeting Reiji Arima she showed interest in him till the mentioning of his heritage as an Arima. Not willing to let him go, seeing an easy way to get his earnings (Ryoko seemed unaware of Reiji's being an Illegitimate child at the time) would try many advances and state he was her new boyfriend, much to Reiji's displeasure.
Finally she would succeed and become pregnant with Reiji Arima's child. Months would pass and Ryoko would send a letter with the picture of a new born child to Reiji. Receiving a call from Reiji later on she stated he didn't have to marry her but would ask for Child Support, and Reiji would reluctantly do so.
This would go on a for months, Ryoko would constantly argue with Reiji for not giving enough money, trying to guilt him that it wasn't enough for her or Soichiro, becoming fed up he stated to her he would not give her any money due to his own limitation and tell her he was an illegitimate child. Therefore he would not get an inheritance of his family's fortune.
During their argument before Reiji's tells her, she could be heard screaming at Soichiro for his constant crying. This would later bring suspicion to Reiji and asks her that if she was giving their son a good childhood. Giving only a hmph in response she would hang up the phone and later disappear for three years till Reiji could find his son.
Ryoko became the tormentor of Soichiro's life for three years. Constantly beating him till he bled, bruising him till he was unrecognizable (labeling him as a monster to other children) and starving him to death where his body was greatly malnourished. One point she even stabbed her son with a pair of scissors, leaving a small scar. Ryoko hated her son because he was no longer a leverage, during those brutal beatings she would scream at her son for being the one to make her suffer for not giving her what she wanted.
When Soichiro was greatly ill Ryoko became wary at his stillness (believing him to be dead) and would try to see if he was still alive. He would scream for her but she would kick him away and leave him. Reiji (who cares for the child) would find a bloody Soichiro in the snow outside their run down apartment would see the horrible condition of his son. Acting as a father for once he would leave his son with Shouji Arima (his older brother) and Eiko Arima care.
Years after her abandonment Ryoko sees Soichiro on T.V. for becoming the nation's Kendo champion she would locate Soichiro and makes him have secret meetings with her in her house, trying to lure him there by telling him his past.
But finally her advantages would fail when Soichiro refuses her, thus she would try to slap him but would hit Eiko. After a brief argument she would leave till she sees both Reiji and Soichiro together on T.V.
Making one last attempt she tries to get Soichiro to reveal where Reiji is. Saying it could be a chance for a family get together. Though he easily tells her off, she slaps him right in front of Yukino Miyazawa and orders him to tell her. Reiji would make his presence known from seeing them and orders her to release his son. Playing coy she would try her advantages on Reiji but gets kicked to the ground, much to her shock. Reiji explains to her that no matter what the circumstances are she will always be that same cruel person she has always been. He tells her about how he knew she tried to use their son and that he was testing her, if she hadn't made contact with Soichiro before both of them were seen on T.V. or that if she didn't even try to find them when they weren't together, Reiji would have forgiven her.
And being proven right he threatens to kill her with a gun, though she believes this to be another childish game of his. But she would be proven wrong from Reiji grazing her at the ear, causing bits of blood. He states that she knew nothing of what his capabilities were and that it was her fault for being the cause of his and Soichiro's suffering. Though she denies this and blames that it was her own misfortune when she was abused by her stepfather and led her to become what she was.
Ryoko manages to run away thanks to her son, who believed despite her actions it was not worth it for her to die. Though despite herself surviving, Reiji stated that if she ever tried to get near Soichiro he would kill her.
Despite Reiji threatening her she would come back one final time after Soichiro's graduation (Reiji would return to America at the time). However unlike her tactics before she asks Soichiro to give her the chance to speak to him one final time, he would agree. She has made a reservation for the two of them. It is likely that Ryoko gave her sincerest apologizes for the things she had done to him and that this was their final good-byes to one another.
This proved to be true when it was mentioned by Soichiro who admitted that if he hadn't agreed, he would have remained in the darkness. With it giving him closure of his tragic past he forgave her.
Ryoko was mentioned by Soichiro sixteen years later after that and her whereabouts remain unknown.
Ryoko was depicted as a beautiful woman and was praised from Tsubaki herself from her good looks (which she mentioned her good looks passing down to Soichiro) she also had long wavy hair that goes past her shoulders. She wore various expensive clothing and was noted to wear a lot of perfume.
Ryoko is a gold digger.(someone who only marries people for their money.) She was an abusive mother to her own child. She is also willing to use dirty tactics to get what she wants as she tries to bribe Soichiro with hints about his past. She was a woman without remose and didn't care what it took to get what she wanted.
Though it is unknown if she continues these actions even since she apologized to her son and disappeared sixteen years later.