By the end of the 21st century, a massive catastrophe ravages Japan, rendering its landscape unrecognizable and bringing civilization's progress to a halt. In the present day, the emperor and his four sons rule the nation with an iron fist. Legend holds that only the prophesied "Child of Destiny" can liberate Japan from the royal family's grip. Sarasa is the twin sister of Tatara, the Child of Destiny. Although she lives in her brother's shadow, Sarasa supports him in every way she can. However, tragedy strikes when the Red King, the emperor's youngest son, and his forces attack her village, resulting in Tatara's brutal death. To shield the townspeople, Sarasa assumes her brother's identity and becomes the Child of Destiny, swearing vengeance against the Red King. As the sudden turn of events takes a toll on her health, Sarasa visits a hot spring to recuperate. During her stay, she meets Shuri, a charming yet mysterious young man. Shuri is captivated by Sarasa because she treats him differently than other girls; meanwhile, Sarasa finds herself unable to stop thinking about him. This casual encounter seals their fate—destined to be bound by war, hatred, and love.