Two sisters.
The elder friendly and warm as the day, the younger beautiful and mysterious as the night.
Inseperable. One could always see them together, laughing together, training together or fighting together on the battlefield.
But their friendship ended one day. The younger turned against the elder.
Hearthbroken, the elder sealed her sister into the moon, later ascending to royalty.
She now rules as a just and noble queen.
But as the thousandt year of her reign comes to an end, so ends peace. The younger has returned. And she is prepared to fight her sister once again.

Tags may vary as the story goes on.