Sumire Saitō (
Sumire's family is originally from Austria, and their family migrated to Japan to serve the Kotobuki family. At some point in time, they changed their surnames to Saitō.
Sumire was brought up inside the Kotobuki household, and she began to play with Tsumugi at a young age. Because of this, she started to treat her as an older sister.
In reality, Sumire had no intentions of joining the Light Music Club. The real reason why she was found in the clubroom by Azusa, Ui, and Jun was because she was ordered by Tsumugi to take the expensive tea set in the clubroom. However, she kept this a secret from everyone, in fear that Tsumugi might punish her if her secret is exposed.
Azusa, Ui and Jun met her at the club room. Sumire knows how to make delicious tea like Mugi. Sumire is the fourth member of the Light Music Club since Ui and Jun joined. When Azusa, Ui and Jun first saw her they thought she was a foreigner because of her blue eyes and blonde hair. Sumire eventually became the Light Music Club's drummer after showing talent in the instrument.
She first appeared in the fifth volume of the manga on the second chapter. Apparently, despite having the same color hair and eyes as Tsumugi Kotobuki, she works as a maid for the Kotobuki family and Tsumugi has given orders to her to put away the club tea sets she left behind but fails to do so. Tsumugi has a middle-aged butler named Saitō (as proven in many chapters), so Sumire may be related to him.
Sumire feels enclined to keep her role as a maid a secret, fearing that Tsumugi would then find out from the others that the tea sets would not be taken away, and she would fire her. In chapter 62, she almost says she sees Tsumugi as an older sister, but kept quiet, so that she would not give away herself.
Sumire was afraid of Sawako after she wanted to take her as her victim to play dress up (before Sumire entered the club). She would feel uncomfortable seeing Sawako around her at first, but she soon got used to her after she entered the club.