Shiina, otherwise referred to by his nickname Shii, is another adult friend of Shūichi and Yoshino. He was Yuki's classmate in elementary school, and he eventually became her boyfriend after her transition and due to her persistence. Unlike Yuki, Shii had many friends in school. He generally just watches over Shūichi and Yoshino with Yuki, but he does sometimes do bold and unexpected things, such as grabbing Yoshino's crotch when the two of them first meet because he feared that she, who was dressed as a boy at the time, might be Yuki's illicit lover in an affair.