Ryoba Aishi is the mother of Ayano Aishi and yandere for Mr. Aishi.
She went to the same school that her daughter currently attends and became obsessed with her senpai. After removing her rival(s), she abducted her senpai and made him love her. At some point, they got married and had Ayano together.
Like her daughter, she's obsessed with her eventual husband. She's killed at least one girl for catching her senpai's attention. It's never stated how much many people she's killed. She kidnapped her senpai and decided that they should start living their lives together, much to his protests.
- According to YandereDev, Ryoba and Ayano come from a long line of yandere women.