Legend of Basara

At the end of the 21st century, a great catastrophe devastates Japan, leaving its land unrecognizable and halting civilization's progress. In the present day, the emperor and his four sons reign over the country with an iron fist. It is said that only the prophesied "Child of Destiny" can free Japan from the royal family's shackles. Sarasa is the twin sister of Tatara, the Child of Destiny. Despite having to live in her brother's shadow, Sarasa supports him in any way she can. However, tragedy strikes when the Red King, the emperor's youngest son, and his army attack her village, leading to Tatara's brutal death. To protect the townspeople, Sarasa takes on her brother's name and becomes the Child of Destiny, vowing revenge on the Red King. With the sudden turn of events taking 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 fascinated by Sarasa as she treats him differently from other girls; meanwhile, Sarasa is unable to stop thinking about him. This casual encounter between the two seals their fate—destined to be bound by war, hatred, and love. (Source: MyAnimeList)