Marika Uruuno is enamored with normality. To fall in love, get married, and build a family—this is her idea of normal. One day, on her way to meet up with her best friends and walk to school together, Marika turns a corner to find them kissing each other. Though shocked to see such intimacy, as her friends have never displayed this kind of behavior before, she decides to think nothing of it. However, her lingering unease is validated when she arrives at her formerly co-ed school, where all of her classmates are now girls. It seems as though Marika has wandered into a world where men no longer exist!

In a panic, Marika heads to the nurse's office to calm down. There she meets Lily Kazami, who is reading a book on parallel universes. Although she is ignored at first, Marika ends up telling Lily about her bizarre situation. Setting aside her disbelief, Lily offers to assist Marika on the condition that they go out together.

Can Marika grow accustomed to a world that pushes the boundaries of normality—and can Lily help her escape it?