Sayu
Sayu and her brother had never been particularly close. They were polite and they worked together pretty well, but she'd always had this nagging feeling that he was just using her to keep up his 'perfect brother' image, to match his 'perfect son' and 'perfect student'. So when Kira apeared and Light began acting strangely, she waited until he was out of the house to ransack his room. The booby-trap was cleaver, but once she made the assumption that there would be a booby-trap, it was fairly easy to disarm. She took the book she found there and went down to the police station. She ducked behind a tree to avoid her brother talking to some woman, and arrived at the station just after Aizawa. She insisted that she talk to L directly and when she finally got to speak to that electronic voice she gave him her name and said, matter-of-factly:
"My brother is Kira. I have proof, but I'd rather give it to someone who hasn't known him all his life."