Step sister (Winrina)

Karina wasn't very interest on going out or something like that since the day wherein her mother died. But she accepted it. She's lucky enough that she have a father who would support her on anything and cheer her up. A lovely precious father.

But one day, her father decided to marry someone. In addition karina was happy for him and just accept it and forget the past. Marrying someone as long as his father is happy.

"oh by the way my precious lovely daughter! You will have a step sister who is younger! She's 20, her name is winter. You'll meet her up soon!" her father said which karina just nod.

What will happen?