Kudou Nono

Nono is a 1st year high school student. She is the youngest of the Kudou twins, and Youichi's little sister.
Hinano and Nono are Youichi's stepsisters by marriage, their mother was the wife of Youichi's father, as such they are not related to Youichi by blood.
Several years ago, when Hinano and Nono were but children, they were sent to live with their aunt. Said aunt is now getting married, which made Hinano and Nono decide that they would move back in with Youichi, and that they would start their high school days at the same school which Youichi attends.

Roughly edited from a Google Translation of the following website: Japanese Wikipedia