Cristy Kawaoka because he's a sicko. it's a way of controlling her, by making her feel ashamed. typical abuser behavior.
Snoopypanda If I hadn't accidentally seen this question before I finished the book I wouldn't have realized that Richie was the one who wrote that stuff on her books. I was really ticked that they didn't have some sort of resolution when it came to Eleanor and her stepdad, like her mom finding out that he was the one who had written that stuff and not Tina from school. The fact that her mother put up with that jackass and put her own happiness above her kids' safety and comfort really ticked me off. That makes her mom almost as big of a loser as Richie is.
Sam I think that Richie wrote those sick messages on Eleanor's possessions because she knew that he was morally defiled. She saw the "Nazi" side of him that no other child saw or wanted to believe. Richie probably wanted to be loved and cared for like any other human being, the only thing that was preventing this was Eleanor. I think that those inhumane messages were a method of ridding his life of Eleanor to be able to live the life that he had always wanted.
Eesha I was very confused too! I couldn't really wrap my head around it. He probably was going to abuse her. I don't really uderstand his actions towards eleanor. All I know is I despise his entire existence.