In the aftermath of a catastrophic event at the close of the 21st century, Japan has been reduced to a barren wasteland, halting all further progress of civilization. The current regime is ruled by an emperor and his four sons, who impose a harsh tyranny over the people. It is believed that only a "Child of Destiny" will possess the power to liberate Japan from the imperial family's oppression.
Sarasa is the twin sister of Tatara, who is destined to become this Child of Destiny. Though she lives in her brother's shadow, she devotes herself to supporting him. Tragedy strikes when the Red King, the emperor's youngest son, attacks her village, resulting in Tatara's brutal death. To protect her fellow villagers, Sarasa assumes her brother's identity as the Child of Destiny and vows to seek vengeance against the Red King.
This drastic change takes a toll on Sarasa's health, prompting her to visit a hot spring for recovery. During her stay, she meets Shuri, a captivating yet mysterious youth. Shuri is drawn to Sarasa because of how differently she treats him compared to others, while Sarasa finds herself increasingly preoccupied with thoughts of him. This unexpected encounter sets the stage for a destiny intertwined with warfare, resentment, and affection.