Toa Azusa

A former magical girl, who attends a far-off school. Due to this, her and Taiga rarely see each other, but on occasion she will take the bus over to check up on her little brother, who attends the same school as Taiga.

Unlike her brother, she is an introvert, and doesn't deal well in social situations.

Spoiler

She is the mother of the real Kanade Taiga (not the nameless protagonist)