Ryoba Aishi

'''Ryoba Aishi is Yandere-chan's mother and the current wife of the father. '''

It has been confirmed from the first basement tape that she is the same girl featured in the mysterious tapes whom The Journalist confronted. She is out of town for 10 weeks for Story Mode because of an unknown reason.

Background
When Yandere-chan's parents were in Akademi High in the 1980's, Yandere-chan's father was Ryoba's senpai. Ryoba was also a yandere, and killed the Phantom Girl with a knife  in the third floor girls' bathroom. As revealed by a series of tapes, her activities - using manipulation, intimidation, and sometimes even violence to bring about the disappearances and expulsions of her upperclassman's admirers - were discovered by a suspicious journalist who had taken it upon himself to investigate the murder when the police were forbidden from conducting a formal investigation. Ryoba was arrested and accused of comitting numerous crimes, but was able to not only deflect the charges but sway public opinion in her favor by playing the part of an innocent girl being stalked and falsely accused. Ryoba used the court case to simultaniously become a media darling and irreparably ruin The Journalist's reputation, and after she was acquitted of all charges she cornered the Journalist and warned him to never cross her again, as it would be too easy to make his death seem like a suicide.

Soon following this, as revealed by Basement Tape #1, Ryoba abducted her upperclassman, tied him to a chair, and forced him into a relationship with her, revealing that her mother had done the same to her own crush, implying that she was a yandere too. Ryoba eventually married her upperclassman, giving birth to a single daughter at around the age of 19. She has no other children other than Yandere-chan.

She has a job related to the game's lore. YandereDev has planned to drop hints about what the job is soon.

Ryoba never moved out of her home town or gave up her yandere habits, as almost thirty years after the investigation she was discovered by The Journalist stalking a young woman fresh out of high school. Realizing The Journalist had returned, Ryoba lured him into an alleyway and ambushed him. He escaped and fled Japan, and it's implied that her ten-week absence is an attempt to hunt him down and make good on her threat. This is why Yandere-chan lives alone during the course of the game.

Appearance
The mother has a very gentle face. She is identical to Yandere-chan, but older. She has the same hair color and hair style as her daughter. When her true nature shows, her eyes are empty and soulless, and she wears a disturbing smile.

Personality
She is a yandere and a murderer. In the original intro, Info-chan gives a hint about it when saying "So, history is repeating itself?" and "It is in your blood, after all" to Yandere-chan, although this intro is now outdated. Being a yandere, she is clingy and paranoid, needing to kidnap her senpai even after getting rid of her rivals.

Another part of being a yandere means that the mother seems to be willing to take serious action to get jobs done, as seen by how she dealt with the Phantom Girl. This was just out of obsession for the father of Yandere-chan. The way she took down a girl with only a knife probably means that she's tough enough to take another student down both mentally and physically.

She also seems at least somewhat cunning if she was able to murder some people, get away with her crimes, and able to kidnap the father. She was able to fool all of Japan into thinking she was innocent and that The Journalist was the villain. She must be very confident and bold to do such things.

Mysterious Tape #3 shows that she was well-rounded and could effectively bully, expel, and keep people from coming to school. Judging by the fact that she usually ran around with a mop and bucket means that she still killed people, so she pretty much used a variety of elimination methods to achieve her goal, unlike Yandere-chan who can just use one, but might not.

The fact that Ryoba never killed The Journalist during the few decades of their truce means that she isn't entirely needlessly cruel towards her goal. She left him alone instead of maliciously attacking a person who's totally helpless, and doesn't seem to kill any regular girls or boys for fun. It's possible that the methods of elimination she chose were simply the best options for her, but hated the rivals too much to actually get rid of them without hurting them in some way. All in all, she seems kind of practical, except for the fact that she kidnapped her senpai after getting all her rivals, not before.

Yandere-chan
Ryoba might have passed down her murderous traits to her daughter, though Yandere-chan doesn't have to kill anyone over the course of the game.

Yandere-chan doesn't have a negative relationship with her parents. The Dev states that she's just indifferent to them. Yandere-chan believes her mother to be a lovely human being, though she may not know what her mother did in the past. Yandere-chan's mother loves and adores her daughter very dearly because she is a physical manifestation of the love between her and her husband. The mother knows about Yandere-chan's lack of emotion.

Yandere-chan's Father
Ryoba's background was revealed in the Basement Tape. During the 1980's she kidnapped her soon to be husband and held him hostage. It is revealed that she extremely loves him, while he doesn't have the same feelings for her back. She eventually married him and had one daughter, Yandere-chan. While they were in high school, Yandere-chan's father was Yandere-chan's mother's senpai.

Phantom Girl
Ryoba killed the Phantom Girl with a knife in the third floor girls' bathroom. The reason for the homicide is unknown, or how dangerous the Phantom Girl was.

The Journalist
Their backstory and how they interacted is told throughout the Mysterious Tapes.

The Journalist can almost go blind with rage when he sees Ryoba, though he still runs away from her after she found him stalking her after a few decades. The Journalist revenge has seemingly failed for now, but he is said to appear in a secret main story mode ending, which implies that he could've gotten away.

Ryoba doesn't care in the slightest for The Journalist, not taking the time to actually kill him. It's understandable to not do so right after the case, which would be suspicious, but she never hunts him down after that.

Unimportant Woman
In Mysterious Tape #9, Ryoba was stalking a woman who flirted with Yandere-chan's father. The woman died in the next tape. She is a very unimportant character as she won't have a name or will ever be a rival.

Trivia

 * Her name was revealed in Basement Tape #1.
 * The basement tape may have implied that Ryoba raped her husband. When asked about this on Twitter, YandereDev said that he would like to address this issue with a tape so it would not be spoiled on Twitter.
 * Ryoba's name is most likely derived from ryōba usuba, type of Nakiri bōchō; Japanese-style vegetable knives. Ryōba is knife with cutting edge angled from both sides, making it easier to cut straight slices. This, however, is only a speculation of where her name is possibly derived from.
 * She never left her hometown, so it was easy for the Journalist to find her after several years.