Sumire Saitō (
Sumire grew up with Tsumugi Kotobuki, although Sumire's family worked as servants for the Kotobuki family. Despite this, Sumire stated that she looks to Mugi as if she were a sister, and takes her demands and requests very seriously. She even refers to Mugi as "Onee-chan" (Older Sister) in High School, Chapter 8. Sumire was Mugi's only playmate, as Mugi's gifted upbringing often led to her not having time to play with other same-aged children.
Being a maid for the Kotobuki Family led Sumire's maid-like instincts to come into play multiple times throughout the year. The girls would often ask for Sumire to make tea, and she would instinctively prepare some for the entire club, of similar likeness to the tea that Mugi would often make.
Sumire took to playing the drums, as she claimed it was a good way for her to relieve her daily stress.
Sumire has blonde hair and blue eyes, very much like Mugi. She adorns the blue-colored ribbon on her school uniform, which was the same color ribbon that the already-graduated original members wore.
Her uncommon hair and eye colors led Azusa, Jun, and Ui to mistake Sumire as being a foreigner. In their first encounter, Jun attempted to speak to Sumire in English, to which she replied that she couldn't speak it and that she was, indeed, Japanese.
At first, Sumire had no intentions of joining the Light Music Club. However, she was found in the clubroom by Azusa, Ui, and Jun on the first day. This was because she was ordered by Mugi to take the expensive tea set in the clubroom. However, she did not reveal her relations to Mugi in fear that if her objective was discovered, the Kotobuki family would fire her.
Eventually, Sumire joined Azusa, Ui and Jun, becoming the fourth member of the Light Music Club. To their surprise, Sumire knew how to make delicious tea much like previous member Tsumugi Kotobuki. Sumire eventually became the Light Music Club's drummer after showing talent in the instrument.
Sumire felt inclined to keep her role as a maid a secret, fearing that Tsumugi would then find out from the others that the tea sets weren't put away, and she would fire her. However, it was later revealed that Mugi only put Sumire to this task to have Sumire join the Light Music Club in an arranged "accident".
In the beginning, Sumire was afraid of Sawako, as she wanted to experiment on her as a dress up victim (a characteristic Sawako has portrayed numerous times). She would feel uncomfortable seeing Sawako around at first, but she soon got used to her after she entered the club.