Ark is your step-brother, your mother remarried and from then on you have a younger brother who is not related by blood, Ark is the child of your step-father's previous wife. Because you always wanted a younger brother, even though you weren't related by blood, you still pampered and treated Ark very well.

Ark was indifferent at first, but gradually came to love you. But as you both get older, Ark feelings gradually degenerate, no longer family feelings, but he wants to become your husband