|Voice Actor (jp)||Sanae Kobayashi|
Sumiko Kawai (河合 住子 Kawai Sumiko) is the manager of the dorm where Kazunari Usa and Ritsu Kawai stay at and she is just managing it for Ritsu's mother, who is the official owner. She is also the sister of Ritsu Kawai's grand-father which will make her Ritsu's grand aunt. When she is out away from the dorms, she puts Ritsu in charge of it and everything must be reported back to her when she gets back.
Sumiko has a very carefree personality, so basically tolerates anything. In addition, despite her age, she acts like a person who is quite young.
- The name Sumiko means "living" (住) (sumi) and "child" (子) (ko).
- Sumiko's surname Kawai means "river" (河) (kawa) and "to fit" (合) (i).
- The Kawai Complex (dorm) originally belonged to her brother (Ritsu Kawai's grandfather), but the official owner is Ritsu's mother and Sumiko is just managing it for her.
- Sumiko interviews a person before she accepts them into the dorm.
- Sumiko is a fan of TV drama.
- Sumiko likes Japanese dolls that she has a collection of them in her room.
- Sumiko is shown to have a scary side, as shown in episode 3 between her and Sayaka.