First Princess

"Diana" is the First Princess of the Sternbild Kingdom, she is promised to the heir of the Kirika Empire. Her health status is what caused the war between the Elves and the Kirika Empire allied with the Sternbild Kingdom.

She is well known for her intelligence and beauty.

History
She caught a disease eating all her internal organs and since there's no cure, once infected, there's a high chance to die from it. Although they still didn't find a cure, they find a way to slow the disease's advance but half of her organs were already rotten. She was put to sleep in order to stop her suffering.

That's when someone received a revelation saying that the Elves of the Kuuderun Great Forest had a cure to all illness. But the Elves' laws forbid them to give it to any human. Facing this refusal the war was declared.

Finally, the Esseba Failo Rheinfall gave some of the elixir to Rou. By drinking it he gained the ability 【Elixir of Blood】. After some battles, Rou send one of his clones to deliver a flask of his blood to the heir of the Kirika Empire with the intention to end the war. The heir received it with the condition to retire its troops, what he did. We can assume that she is now healed.