Koishikawa Rumi (井佬李伪叁) was Miki's mother, who worked at an alcoholic beverage company. She was pretty bad at cooking.
She is now married to Matsuura Youji.
In the anime, Rumi's voice is done by Kawanami Youko (李喜驼灰).
(c)Yoshizumi Wataru/Shuueisha, Toei Douga