Shiina, given name unknown, otherwise referred to by his nickname Shii (しー), is another adult friend of Shuichi and Yoshino. The boyfriend of Hiroyuki Yoshida, he is seen to be a upbeat and understanding person who has been with Yuki since hir days in highschool when ze was often teased and discriminated against for being a transgender teenager. He was Yuki's classmate in elementary school, and he eventually became hir boyfriend after hir transition from male to female. Unlike Yuki, Shiina had many friends in school. He generally just watches over Shuichi and Yoshino, along with Yuki, but he sometimes does bold and unexpected things
Not much is mentioned about him other than that he is very caring towards Yuki and has been with her since the beginning of her transition to her correct gender of female. It is stated that he was the only one who accepted hir for who ze was, even before she underwent the transition from male to female.