Na Bibi and her only friend Dahee, both bullied by their classmates, have been enduring a painful middle school life. But after turning 17, Na Bibi gained the ability to transform like a butterfly and be reborn infinitely with a different appearance. With a brand-new pretty look, she is now ready to start afresh as a high school student. But her transformation stirs tensions with Dahee who disappears on her. Struggling with her identity, Na Bibi enters high school. She coincidentally ends up in the same class as Bang Yeonwoo, a student from the same middle school...