The Love Is so Deep That It Lasts Only a Moment

He is the concubine of the palace. Everyone knows that he is ruthless, vicious and cruel, but they don't know how he could live safely in the palace that eats people without spitting out their bones if he is not ruthless. How can he protect his weak and incompetent sister? He can only make himself strong. Only when he is strong enough that others can't shake him can he protect the people he wants to protect. What should he choose when he finds out that his weak sister is the devil that the court has captured to make it difficult for him to sleep and eat?