At birth, every person in the world is born without a defined gender. However, when a child turns 12, their body starts to develop into their desired gender. This process doesn't apply to Hinase Arima, who has yet to experience any physical changes even after reaching the age of 18. Despite this, they are content with life as long as they have their two childhood friends: Ritsu Kaga, an joyful and cute girl, and Shiori Takayama, a tall and stubborn boy.
As Hinase approaches their final year of high school, they expect things to remain unchanged. But, their life is turned upside down when both Ritsu and Shiori confess their love on the same day. Because they've never felt any romantic or sexual desire, Hinase doesn't know how to respond to both of their confessions. However, with time running out, Hinase must make a critical decision soon: to choose between becoming a boy or a girl.
