Mahiru is a shy and timid girl who often has troubles speaking for herself. She is easily subject to bullying, and is often defenseless.
It can also be noted that Mahiru and Shinya's names also have polar opposite meanings, with Mahiru's (真昼) being "midday" and Shinya's (真夜) being "full night". Mahiru / Shinya wears black and white socks, possibly to represent this split personality. As well, her school uniform seems to have a somewhat odd color scheme.