Kobeni is the "ultimate average high school first-year student." She handles the cooking and all other household chores. On her 16th birthday, a young man named Hakuya and Mashiro suddenly appear in front of her, in which it turns out that Hakuya is her fiancé and Mashiro is her future sister-in-law.
Kobeni is a slightly pale-skinned girl with shoulder-length salmon pink hair that is tied in two pigtails, violet eyes (her eyes changed to violet after Hakuya Mitsumine gave her half of his powers to save her life), a scar from the accident involving herself and Hakuya, her large breasts and "childbearing hips" are noted by several characters and she has also been described as short.
She normally wears school clothes.
Kobeni is a generally sweet, delightful and optimistic girl. However, she is capable of being a bit scatter-brained at times. Even when something doesn't go exactly as planned, she manages to shrug it off and carry on. She can take everything in her stride. She oddly seems to use shopping as a method of relaxation, for example: during Episode 1, after having the bombshell of betrothal dropped on her, Kobeni quickly runs from the house, with the excuse of going shopping to feed unexpected guests. Everyone around her has high expectation and different motives towards her, she has a heavy burden of feelings in her life, too many people normally think she can used for many reasons.
Kobeni has one older sister named Benio Yonomori where the two of them grew up in the city and she was arranged to marry Hakuya Mitsumine by her grandfather, She often went to visit Hakuya and the rest of the Mitsumine household when she was little.
When she was visiting Hakuya Mitsumine, the two of them had decided to play in the woods. Kobeni fell down a cliff and Hakuya fell down to save her. Both of them were injured severely, although Hakuya gave some of his Inugami powers to keep her alive long enough so that he could go get help. Kobeni lost her memory in the accident, and forgot about Hakuya and his family. They didn't visit the Mitsumine household after that, so she knew nothing about them.
On her sixteenth birthday, Kobeni met Hakuya Mitsumine again, and met his little sister, Mashiro. She was then told that Hakuya was her fiance. She has not yet learned anything else of their the past, except that she had known him before the accident.
Hakuya is the main protagonist and Kobeni's fiancé who start out as very distant as the majority of their initial encounters are laced with heavy awkwardness. As the series progresses, Kobeni becomes closer to Hakuya and they both talk to each other more frequently. However, Kobeni continues to maintain her distance between from Hakuya since she is still uncertain about having him as her fiancee. Kobeni is also quite dense about her romantic feelings towards Hakuya as she often blushes when he bluntly compliments or states his affection towards her. Eventually, both Kobeni and Hakuya begin to understand each other, they are comfortable around each other and they share some memorable/romantic moments together.
Benio is Kobeni's older sister who has a huge sister complex. Kobeni does love her sister dearly, and shows a high level of respect, even calling her "onee-sama", although this could just be because Benio forced her too. Despite the good relationship they have, Kobeni finds Benio over-bearing, and tries (in vain) to get her to stop. Kobeni suspects that Benio's over protectiveness is because of the incident that happened in the mountains when they were young.
Mashiro is Kobeni's future sister-in-law whom she is rather careful about what she cooks since Mashiro dislikes foods such as fermented soybeans and spicy curry. Mashiro starts off as being quite blunt and "adult-like" towards Kobeni. As the series progresses, she slowly drops this guard and reveals her child-like personality. She is slightly jealous of Kobeni's appearance especially her breast because she thinks that her breast is the ultimate weapon since many of their male classmates likes her very much
Mayura is Kobeni's good friend who are often seen walking to school together and they frequently talk to each other between classes. Mayura even goes as far as lending Benio Yonomori her company's helicopter to rescue Kobeni when she's missing in the mountains. However, most of the time she gives useless information and advice to Kobeni.
- The name Kobeni means "small" (小) (ko) and "red, vermilion, crimson" (紅) (beni).
- Kobeni's surname Yonomori means "night" (夜) (yo) and "forest" (森) (mori).