On a world far removed from the Earth, there is a certain kingdom that's brimming with smiles. Fate thrusts young Princess Yûki Soleil, filled with idealism, joy and innocence, into a station in life for which her most endearing qualities are ill-matched. Her kingdom faces grave danger as the Empire threatens the realm's security. Meanwhile, on the opposite side of the conflict, an imperial soldier known as Stella Shining hides behind a facade. However, a time may come where her mask cracks, potentially costing her everything. Princess Yûki and Stella's paths will cross, and the fate of nations will follow.