Saegusa Ryouka♀

She is a career woman who runs a design company. She is raising Mizuki single-handedly after her husband's death, but her hard work has diminished the contact between parent and child.

Mizuki has been attending a swimming school with her, which she used to do when she was a student. Mizuki does not need to go to the school, but reluctantly does so as a way for mother and daughter to share skinship.

She is now in a platonic relationship with the chief instructor, Shinohara, with the intention of getting married.

However, perhaps due to the stress of her job and her relationship with Shinohara, which she is unable to keep close, she is not able to keep her mature body in check, and often spends her days masturbating in the locker room.

[From official site]