The elder Daidou sister, an easygoing, perverted, and seemingly irresponsible girl who works in research and development for a big company. She fell in love with her younger sister, Sayo, when they were teenagers, but they grew apart after Ayumu devoted herself to her studies. Believing that her sister, who had grown distant, hated her, Ayumu decided not to confess after getting into university, as originally planned, and instead left for her classes, leaving her sister and first love behind. Years later, they reunite thanks to a dating website. While at university, Ayumu dated Tsubomi Kagaya for almost a year, but she was dumped because of her distant behavior and enduring infatuation for her younger sister.