Fumio Usui (雨水 文緒 Usui Fumio), Kenta's mother, is generally depressed and has trouble keeping jobs, usually being fired after one of her male co-workers sexually harasses her. It was speculated by Anju that she has overactive pheromones, which is the reason why men are drawn to her.
Fumio has shoulder length black/brown hair and generally wears t-shirts and skirts. She has depression due to her inability to keep a job because the men keep trying to get her to sleep with them as she releases a strong pheromone which makes her incredibly attractive.
Fumio is a young mother, having gotten pregnant at the age of sixteen by her high school boyfriend, Shuusei Iizuka. Her mother was furious at this, ordering Fumio to get an abortion, but Fumio refused. During her pregnancy she is abused by her mother, verbally and physically, and after his birth, her mother ignores Kenta, only speaking to him long enough to yell about him being a disgrace. To protect him from getting hurt any further, Fumio took Kenta and fled to Shiihaba City to start a new life.
In the first volume and second episode of the anime television series, Karin bites Fumio, injecting her blood and leaving Fumio cheery, energetic, and with a great increase in self-confidence. It is later speculated that Karin's blood makes people who they want to be. The sudden change in Fumio's behavior, coupled with the strange marks on her neck, makes Kenta suspicious about what Karin did to her that night and that was the first thing that led up to Kenta finding out about Karin and her family. Even though Fumio's mother was mean to her and Kenta, Fumio returned to take care of her when she became ill.
- Despite the pain her mother put her through because of her teenage pregnancy, Fumio is grateful to have had Kenta.
- Because of how badly her mother treated Kenta, Fumio was happy to learn he was loved by someone other than herself (Karin).
- Every leap year, she tells Kenta that he's a year older.
- It annoys him.
- It seems to be the only joke she tells.
- Fumio is a D cup.
- When Kenta announced he planned to marry Karin, Fumio was shocked; mostly because she thought the two of them had sex and were getting married because Karin was pregnant.
- This horrified and embaressed Karin, who Fumio asked about the due date.
- Kenta was annoyed, since didn't plan on making the mistake she did with his father.
- After getting employment that didn't lead to sexual harassment, Fumio noticibly became more cheerful.