Мацуя Місакі

The attractive and intelligent recruit to the Department of City Security, Matsuya is pragmatic and fiercely independent. She is also talented and vicious at repelling Iwata's frequent leers and advances. The manga reveals that she and Iwata were college classmates and that, to her embarrassment, she bears him some genuine affection. She grows closer to Iwata as the series progresses, striking him far less frequently than normal. The only time she seems to feel the need to do so is when Iwata is being idiotic even by his standards, such as trying to track down Excel by telling a young woman that he's looking for "Naked women".

She is also one of the few people in the series that has any sense at all. (Source: Wikipedia)