Yoshino, the other protagonist, is tall and masculine, and at the beginning of Hourou Musuko is a fifth grader in Shuuichi's class. Otherwise known as Takatsuki-kun by her classmates, she expresses a desire to be male and usually refrains from dressing in traditionally feminine clothes such as skirts or dresses, in spite of her mother's insistence on buying them for her. Shortly after meeting and becoming friends with Shuuichi, Yoshino cuts her hair to a very short, boyish style, giving her the appearance of a boy her age, especially when she dresses in a male school uniform. Like Shuuichi, Yoshino becomes increasingly concerned and resentful about her changing body due to puberty. She even goes so far as to buy a garment to flatten her chest so that she does not have to wear a bra.

While Yoshino would like to dress and act like a boy all the time, she usually abstains from doing anything overt which would draw attention to herself such as going to school in a male uniform once she begins junior high. However, she does on occasion dress in a male school uniform and goes to neighboring cities presenting as male, and during one such time enjoys the fact that she is hit on by an older woman. Yoshino wants to look "cool" if she can, wearing clothes which make her look less like a girl. When teased by others, Yoshino is prone to getting emotional, and is also known to get violent on occasion. Yoshino takes up an interest in basketball after entering junior high school, and joins the girls' basketball club with Chizuru Sarashina. In junior high, Yoshino grows her hair out after a comment by Saori, but later cuts it back again to a short, boyish style. Her family consists of her father, mother, older brother, and older sister.

Towards the end of the manga, Yoshino decides to take up modeling and grows her hair back out. She stops wanting to be a boy and feels some guilt over this towards Shuuichi, who unlike her still identifies as a girl. When the two meet again after a while of no contact she finds herself attracted but nothing comes of it due to Shuu already being in a relationship with Anna.