Her name is actually mentioned once in the series by Yoshitake's older sister as "Mei" in the story 'High-school Boys and Siblings'.
Her personality is very sadistic, she has the strength of approximately a teen gorilla and is most likely targeted for pranks by the protagonist trio.
She is short tempered and wears her hair in twin tails. Her approximate age is 16 since she is in the 10th grade.
She only talks to her brother about once a month and they share a distant relationship.
Her panties appearently always get stolen by boys (mainly the main trio) but they were also stolen by Hidenori's older brother Yusuke.
She tends to get overexcited when anything good befalls her (example: Episode 8, Arc: Highschool Boys and Tower where Mei throws her bag far up a tree. Note: this Arc also features an example of her monstrous strength).
However, despite her strength and brutality, many characters (maybe including her own brother) are really worried about her safety. In Episode 6, when she goes to Sanada North's student council and talks about her problem to Karasawa and Motoharu (which she explains that a boy, who confessed to her, hit her and he wants to meet again this afternoon), Motoharu reacted first and said he will go accompany her, but canceled when she told the reason as to why the boy hit her. After the meeting with the boy ends with nothing happening, both Karasawa and Motoharu and surprisingly Hidenori and Yoshitake, who were also listening, came out from their own cover and said 'We were worried for nothing'.