Kiyoka is a childhood friend of Kouta. She is well acquainted with Kouta's family and on friendly terms with his mother. Kiyoka is also a honors student and is very popular in school. She is a member of the student council, a reputable athlete, and maintains very good grades. Kiyoka is a rather good cook but she is rather clumsy with knives. She is also very sharp and observant.
Kiyoka initially dislikes Shigeaki and claims that he is giving Kouta bad ideas.
During junior high, Kiyoka's parents had a divorce. She seeked Kouta for comfort and strength to pull through the ordeal. Since then, she developed feelings for him.
Kiyoka is rather domineering towards Kouta. She often drags him around without paying heed to Kouta's wishes. Kiyoka is also very sharp and she noticed Chieri and Mamiko's interest in Kouta. She is highly suspicious about Chieri's disposition towards Kouta and she attempts to confront Kouta several times without following through.
One day, Kiyoka followed Kouta to his home to confront him and attempt to voice her suspicion. They were interrupted by his mother and she mentioned that she couldn't prepare lunch for him. Kiyoka volunteered to make lunch for him and later attempted to reveal that she loved Kouta.
Later, Kiyoka confided in Kouta explaining that Shigeaki had confessed his feelings for her. She was taken by surprise and decided to ask for Kouta's advice. Kouta took her situation as a mirror of his situation with Chieri and Kiyoka.
When Kouta skipped a class to spend time with Chieri, Kiyoka witnessed them and confronted Kouta about it. She demanded that he end his relationship with Chieri.
If Kouta does as she says, Kiyoka tears Kouta away from Chieri. If he decides to console Chieri, Kiyoka walks in on them and she got into an argument with Chieri. They eventually became friends.
If Kouta decides to tell Chieri, he tries to figure out his next move. Kiyoka confesses her feelings for him and argues that his relationship with Chieri will be very difficult. If he decides to follow through with his relationship with Kiyoka instead, they graduated together and Chieri moves on.