Saitou Kayano is the principle female character in the series and the reader basically follows her life and her point of view. Kayano is a pretty normal girl. She's not outstandingly pretty, so she doesn't attract a lot of attention. Her father passed away 8 years ago and she's living a content life with her mother. She worries about what a normal girl worries about: her crush and she has the support of her two best friends.
In the beginning, Kayano is shown to be someone who's extremely shy and is in constant need of her friends' guidance. She doesn't voice out her opinions because of her fear and gets easily pulled into being Takeru's servant. However, while she still has her shy moments, she slowly gets rid of her fear. She begins to yell out her thoughts and can be pretty stubburn. She's even seen slapping Takeru a couple of times.
Kayano experiences many insecurities, especially those regarding her relationship with Takeru. Many of them makes her act rashly or jumping to the wrong conclusions. However, as the series progresses, she slowly gains more confidence in herself. In the end, she becomes a very determined women who places her trust in those she cares about and in herself.
What attracts people to Kayano is her endless compassion. Takeru often rants about Kayano exhausting herself with other people's problems, but that's just the way she is. If she sees injustice being done, she will try her best to put an end in it and sometimes even sacrificing herself. Really, she's a very well grounded women who knows right from wrong. That isn't to say that she doesn't make any mistakes (because she does), but she would always try to make up for them.
While it wasn't the case in the beginning, we, as a reader, begin to see what a strong character Kayano truly is. She doesn't have any magical powers or super human strength. She affects and changes the life of those around her by simply caring for them and that, is very admirable.