Former Kano of Mizuto. The maiden name is Ayai. The female protagonist of the series. Moves in with her ex-boyfriend Mizuto Irido when their parents remarry. Loves reading, especially mystery novels. Used to be quite introverted and shy but put in the effort to socialize and become popular after entering high school.
She resented her gloomy middle school past self with little to no knowledge about fashion. Before going to high school, she wanted to change and started to look up fashion magazines. She learned how to dress up properly, to putting make-up on herself and so on. She is dressed up like a typical high school girl with varying fashion from dresses to jeans.
Due to her past, she wants to take a 180 degree turn from her gloomy middle school self to an honor student whose able to get along with others. From time to time, her honor student image slips off especially when asked about Mizuto Irido. She highly thinks of herself because she managed to change her personality unlike Mizuto who stayed as a loner. But when faced with overwhelmed pressure, her personality shrinks. She has hobby of reading, and mainly read detective novels.When she was in junior high school, she had few friends and was a shy person who was always read book, but she succeeded in making "high school debut" as an honor student who was interested in going to high school.
Before her mother remarried to the Irido family, her name was Yume Ayai. Her father was so busy at work and didn't really cared about their family which is why her mother decided to break up with him. She also became Mizuto's girlfriend during their 2nd year in middle school until breaking up before they graduate. A month later, her mother announced that she was going to be re-married without her knowledge that her mother was going to be re-married to the Irido family.
In academics, mathematics she is at the double-digit level of the national mock exam, and even in high school exams, it is excellent enough to compete with Mizuto for the top grade.
Yui's mother was also a single parent, but unlike Mizuto, who lost her mother before she became aware of it, she remembers her father who divorced her mother.
- Yuni Irido:Yume's biological mother. Her previous husband was too busy with work and didn't associate himself much with the family led to her decision to break up. She became a single mother who single-handedly raised and supported Yume throughout her middle school days until remarrying to Mineaki Irido before she entered high school.
- Mizuto Irido:Yume's ex-boyfriend back in middle school. A month later after breaking up with him, she became Mizuto's older sister.
- Akatsuki Minami]]: She is considered as Yume's bestfriend. All Yume's problems about her love are discussed with her. They often talk about their pasts and think they had similar experiences.
- Kogure Kawanami:Kogure became acquainted with Yume due to being Mizuto's "self-proclaimed" friend of his. Often teases Yume and Mizuto when they are together pairing them up as a couple.
- Isana Higashira:Both Yume and Minami tried to help her bear fruit in her love. Despite their efforts, it ultimately failed which is why they decided to become friends with her instead.
- Mineaki Irido:Mizuto Irido's father who later on became her step-father. He became a father who knows how to distance himself without prying too much on her daily life. Often gets asked by Yuni to agree with her.
- Sakamizu Maki:A tall girl with short haircut from the basketball team. A part of Yume's circle of friends in which she usually hangs out with at school.
- Nasuhana Kanai:An always sleepy-looking girl from the karuta club. Also a part of Yume's circle of friends in which she usually hangs out with at school.
- She knows the fact that step siblings can get married but doesn't want to voice it out. (From Volume 1, Chapter 2 of the Light Novel)
- She was born on the same year, same month, same day as Mizuto's.
- Yume was 30 minutes older than Mizuto.
- Her bust size is D.
- She has a habit of running wild once she get excited.