Mahiru is a shy and timid girl who often has troubles speaking for herself. She is easily subject to bullying, and is often defenseless.
When the sun sets, Mahiru's alternate personality, Banba Shinya, appears. Shinya is the complete opposite of Mahiru, and refers to herself (or even himself) as "ore (ä¿º)", which is a rather rough masculine way when referring to oneself. Shinya has an aggressive and borderline insane appearance. In chapter 16, Mahiru mentions that Shinya is somewhat concerned about their weight.
It is revealed that Shinya came through an experience where Mahiru was kidnapped by a certain man and forced to be photographed. From that, she found escape from reality by finding out about her second personality, Shinya, and eventually killed her captor.
It can also be noted that Mahiru and Shinya's names also have polar opposite meanings, with Mahiru's (çœŸæ˜¼) being "midday" and Shinya's (çœŸå¤œ) 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.