Sana Kaizu

海津沙奈

Sana is Takumi's younger step-sister by one year who lives with him, though there is no blood relation between them. She most often has an active personality when awake, though still has problems getting up for school during the week despite now being in high school. Her best friend is Chiwa Amano who hangs out with her constantly. Source: http://en.wikipedia.org