Ruthless Brother and Fearless Sister

Society has different types of levels, First Class family, second and third. Each one of them possesses an incredible power they hold.

Clark Vascana who owns the "CS group Company" was a World Class Rich man also known as "Cold Blooded King" which refers to his ruthless behavior towards people who dares to offend him. Born with a 1st Class Family, Vascana which has the most powerful wealth in their country, not even the country's presidents have the nerve to disobey him. Clark was always being rumored to be a lover to the World Famous International Designer Stephanie V. Her background information was full of secrets along with her full name. People who seek to find out her true identity never had a good ending.

What really os their relationship?
What is really Stephanie V's identity?
What will happen if the world knows that their siblings in blood? How did the rumored start?

PS: this is a male and female lead.