The male protagonist of the story and known as "Yankee-kun," Shinagawa is a short-tempered delinquent who does not like to be bothered and has no plans for his high school life until he meets Adachi. At first he is constantly annoyed about her repeated attempts at making him come on a school field trip until he learns about her past and her resolution to become a class representative. He is also an honorable person who will try everything to protect others. His best subject is math.
He has a love-hate relationship with Hana Adachi, liking her due to her nature to help others no matter what, but becoming annoyed with her due to her idiocy, lack of common sense, and forcing him to help with her bizarre plans and antics. He suspects that she is constantly with him because she likes him, but whenever he asks her about it, she ignores the question or acts ignorant on the subject. In the bonus chapter after 53, It was shown that Shinagawa decided to attend Mon Shiro only after seeing a beautiful girl at his entry exam (confirmed in chapter 61 to be Hana without her glasses and loose hair). Chiba, Izumi, and Akita were also presented. Shinagawa, although he always bicker with Hana, would do anything so that he won't hurt or upset her. Like, not telling her who he likes (which is obviously her, without glasses and with loose hair).