Birthday: October 31

B-ko is a rich, affluent young woman who is a serious megalomaniac.

She has a one-sided rivalry with A-ko who mostly ignores her and wonders why she even tries to fight her. B-ko is unrelentingly jealous of A-ko's ability to be likeable and carefree, and also 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 chalks up her newfound crush on C-ko as 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 and always picked on C-ko, much in the way that someone with a 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.