Uchi no Heika ga Shinmai de.

Shuka, a princess of the red-summer kingdom, was raised in a very sheltered environment in the inner palace. As her fifteenth birthday approaches, her father and brothers die one by one because of a sudden outbreak of disease, and the kingdom has to find a new king...! Supported by Zen, a military officer who serves as her retainer, Shuka has to face the challenge of a role she knows little about.

(Source: Antisense)