REAL PURPLE

From NOIR:

This is the story of two siblings, Joo-won and Hee-won, and one man determined to take Hee-won's heart. Both of Joo-won and Hee-won feel isolated after their parents separate due to infidelity and remarry, placing both of them in new families. However, Hee-won's new step brother, In-hyuk, notices Hee-won's suffering. Is he determined to take care of her, or is there something more?