She was a kind and shy girl who is in love with Handa.
After she tried to commit suicide she became a scary character and was always stalking Handa, and laughing maniacally.
She was a normal girl that fell in love with Handa when he gave her a new eraser (hence her nickname "eraser"). In chapter 4, when the rumor that stated that Handa had a beautiful girlfriend, Miyoko went insane, wrote on Handa's desk 氏ね (shine) which was interpreted as a death wish for him, but later it is discovered that it was wrote as "I will die". Later Miyoko is trying to commit suicide since she can't endure that Handa has a girlfriend. But Handa saves her by accident trying to replace his desk and saying "I'm sorry" out loud; Miyoko thinks it was directed to her but it was for the desk Handa tried to replace; then when she met Handa's "girlfriend", Miyoko relives to learn that Handa's "girlfriend" is actually Handa's mother who were ask to come to school in regarding of Handa's situation at school due to this misunderstanding rumors.
After this incident, she got a yandere personality and her face changed into one of a degenerate. She became the president of the girl fans of Handa and protecter him by giving a lesson to the fans that she considered an annoyance to Handa.
She often stalks him and has a yandere personality towards him.