Everyone in the world is born genderless. But when children hit their 12th birthday, their bodies alter toward their desired gender. One person is an exception to this phenomenon: Hinase Arima, whose anatomy has yet to change upon their 18th spring. Nonetheless, they are satisfied with this, as long as they have their two childhood friends—the joyfully cute girl Ritsu Kaga and the stubbornly tall boy Shiori Takayama.

With their last year of high school on the horizon, Hinase expects that their life will remain unchanged. Yet, this expectation is quickly swept away when they are confessed to by Ritsu and Shiori on the same day! Having never held romantic or sexual desires, Hinase is clueless on how to answer both of their confessions. However, time is running out, and Hinase must soon make the crucial decision: to choose between becoming a boy or a girl.