Sakura Yukari

The protagonist's uncle's wife. That is, Kyouko's aunt by marriage. A shrewd woman who runs the Sakura family, landowners in Setagaya.

The reason the freeter protagonist can live in a fairly stylish apartment is because she's the building's owner.

She seems to have a long-standing feud with Yoyogi Kamo, the headmaster of Yoyogi Married Women's Academy.