Birthday: September 28

The female lead of the series. She has been in love with the handsome and genius Irie Naoki since their first year in high school after seeing his speech at the opening ceremony. After their newly-built and poorly constructed house was destroyed in a mild earthquake, she and her father moved into the Irie household, her father being very close friends with Naoki's father since they were in school. It is eventually revealed that Naoki has always been in love with her. Kotoko is not very smart, having been in Class F for all through high school (students are sorted by abilities and Class F is the lowest) and being in the department in the university considered as Class F. She is however very spirited and Naoki once says how he can do 90% of the things in the world, and she can do the 10% that he can't. She usually ends up in trouble and Naoki always saves her. She decided to become a nurse so that she could work alongside Naoki.