As time passes, more and more teenage girls are undergoing the emergence of "tertiary sexual characteristics," which involves a swift masculinization of a specific region of their external genitalia. Ooi Haruka is one of the girls impacted by this phenomenon and has kept her bodily changes hidden from everyone except her family. However, a humiliating occurrence with her crush on a crowded train leads to her discovery by a group of students who call themselves the "Swing Girls" or "Bra Girls." To her disbelief, they are privy to her confidential information!
