Yuko Watanabe is a second-year student of Class 2-A at Menjō High School.
Nicknamed the "Madonna of the Library", Yuko is a living legend amongst the student body due to being shy and quiet in nature but possessing a "dynamite" body and a D-Cup bust.
In reality, however, Yuko actually only possesses an A-cup bust with a 78 centimeter waist. Frustrated with her body's lack of developement, she began wearing pads in her bra to increase her apparent bust size and continually increased the size of the pads she wore as she gained more attention from her classmates.
After witnessing Hitoshi's ability with computers, Yuko visits his house with the intention of asking for help in "reloading the teacher's salary and student profiles" which she claimed she had accidentally copied onto a Floppy Disk and deleted the original computer file. In reality Yuko intended to use a virus stored within the floppy disk to alter the breast size data on every student record within the school to hide her actual breast size.
Hitoshi and Saati unwittingly deliver the virus into the school's servers and discover that they had released a virus into the system. Accessing the server from school, Saati confronts and defeats the virus as Hitoshi deduces that the creator of the virus was Yuuko herself.
Confessing that she had created the virus in an attempt to cover up her actual bust size data, Saati reassures her that she is still as beautiful with A-cup breasts as she was with D-cup breasts.
- By the time she had approached Hitoshi, Yuko was wearing over tewlve centimeters of fake padding in her bra.
- Saati was actively intimidated by Yuko's D-cup breast size and becomes depressed when comparing them to her own.