In Geneutrum, males and females are forced to live in two separate cities. Females inhabit City XX, while males are confined to City XY. Any contact between the two is strictly forbidden-indeed, Geneutrum itself denies the very existence of two sexes, labelling them instead as different species of humans. It claims equality and neutrality, promotes same-sex relations, and executes anyone who dares to resist. Cael, a girl whose heart has been drained of emotion by relentless oppression, works alongside her close friend, Aeris, as a guard in City XX. By chance, she encounters her twin brother, Lumin, for the first time in twelve years. His presence rekindles life in her heart-only to be extinguished once more when she learns he has been murdered. Determined to avenge him, Cael sneaks into City XY. There, she meets Fiax, a male commander unlike any other. Instead of killing her, he helps her. Forced to escape by his side, she discovers for the first time the meaning of love and desire. Together, they fight to survive-and perhaps to bring down the entire system.