Daitokuji, Biko

大徳寺美子

B-ko is a wealthy, affluent young woman who is a serious megalomaniac.
She maintains a one-sided rivalry with A-ko, who mostly ignores her and wonders why she even attempts to fight her. B-ko is relentlessly jealous of A-ko's ability to be likeable and carefree, as well as of her deep friendship with C-ko.
B-ko immediately becomes interested in C-ko when she and A-ko transfer to their new school. Her interest turns into obsession, though she attributes her newfound crush on C-ko to simply wanting to be her best friend instead.
Through flashback, we learn that B-ko was a horrid, ugly little girl with a mean streak who always picked on C-ko, much in the way that someone with an unknowing childish crush might tease someone they liked. Not much has changed as she got older (save for her looks), and B-ko's desire to be friends with C-ko turns into actual desire, though she probably is not all too aware of this.
She is rather intelligent, as she has the abilities to design and construct several mecha and mechanical suits for fighting, but B-ko's scheming nature and mania for C-ko makes her appear to simply be a crazed stalker with a crush and too much time and money on her hands.
B-ko says that she will take on the role as the "bad guy" to A-ko's "hero" status since people see her as a villain anyway. She is not necessarily a bad person; B-ko just does a lot of bad things.