Kumiko is Haruka Kotoura's mother. She is a complex character who we are constantly finding more and more about.
She is a plain woman with long black hair. Before Haruka's power manifested, she wore a bright and cheery expresion. After, her expression was cold and unforgiving, as if the entire world was at fault.
Kumiko's motivations are hard to understand. In her words, she is, "A weak mother." She pushes her daughter away, partly out of anger and partly because she does not feel that she is prepared to be her mother.
She used to be a happy-go-lucky woman who was overenthusiastic about life. But when raising Haruka proved difficult due to her supernatural ability to read minds and her husband gradually ceased to come home, she buckled under the pressure. She became openly bitter, and due to her drinking in the final episode we learn that she is an alcoholic. She was difficult with her father as well, acting like a brat.
While she is a weak person, we can also conclude that, at the core, she tried to do good.
Her father became rich at some point in his life, so it is not unreasonable to conclude that she grew up in a rich family.
At some point, she married her husband and had her first and presumably only daughter, Haruka. They were a happy family for a short time, but eventually Haruka's ESP began to manifest. At first, there were no problems. Once Haruka began to read the minds of those around her and blurt out what they were thinking, it began to tear the family apart. The breaking point was when Haruka exposed both parents for cheating on each other. After that, it is implied that the two either separated or had a divorce. Because she felt she was a weak mother, and also out of anger at Haruka, she pushed her daughter away. She sealed it by saying, "I wish I had never given birth to you."
Little is known about what Kumiko did after that. She dated at least one man after that; based on her conduct it is easily presumable that she dated others as well.
At one point, she observed Haruka with her friends, but was still apathetic to her and would not meet or forgive her, stating to the Head Priest that if he were to get any closer to Haruka she would ruin his life, just as she did Kumiko's.
Despite Kumiko's cold and bitter front, at the hotel/restaurant when Haruka is there with her friends, Kumiko throws a punch at Manabe when he talks about spending the night with her daughter. Kumiko scolds Haruka, telling her that liking a pervert such as him is bad taste. After realizing she'd let her motherly instincts shine through, she quickly left.
In the last episode, she was waiting in Haruka's apartment for her. She started out overbearing and controlling, drinking a great deal and being cruel to Haruka. But after being fed up, Haruka stood up to her. She tried to hit her daughter, but Haruka predicted it and ducked. She pushed her mother back, and she fell on her bed. They both picked up a pillow and tried to bludgeon each other. After a time, both grew tired of it and made up in a way. Soon after, she fell asleep. She dreampt of the night she left Kotoura, and it is revealed she cried and called herself a weak mother. She said to herself over and over, "I'm sorry, Haruka." The next morning, she had left. But she made for her daughter Over-Easy eggs, which she made the first time Haruka's mind-reading manifested. In the credits for the finale, she is shown again with Haruka, eating in her apartment.
In the begining, the two had a very good mother-daughter relationship. But after Haruka's power reared its head, she became very conflicted and anxious. She at first tried, in vain, to find out what was happening with her daughter, but after any logical reason was proved false, Kumiko left her daughter out of anger. Kumiko always felt guilty, from the moment she left. It seems that the two repaired, or at least began to repair their relationship, during their meeting.
"I wish I had never given birth to you."
"I'm sorry, Haruka!"
"I'm sorry I was such a weak mother!"
Based on the state of her house in the first episode, it can be presumed the Kotouras were somewhat wealthy.