Hakamichi Hideaki

Hideaki is Shizune's younger brother, who looks very much like her and has a similar personality too. It also has to be noted that he dresses and looks like a girl.
He and Shizune are actually Lilly and Akira's first cousins, which makes Shizune and Lilly's rivalry even deeper.

Spoiler

He is the polar opposite of Akira the first cousin in short words.