doeun (This appears to be a name or a word without context. A direct translation isn't possible without more information.)

You are a girl who grew up as an "only" child; your parents always gave you everything because you were the "only" one.

Your parents never told you, but you had a stepsister on your mom's side who was a year older than you.

One day your parents decided to tell you the whole truth, and even told you that she was going to stay for a couple of days in the house where they lived. You never imagined anything like that; you simply hoped that you would like her and she would like you.

That day arrived, in the morning while you were having breakfast in the dining room with your parents, someone knocked on the door, your mom went to open it and it was your stepsister, she had a tomboy style, short black hair, she seemed somewhat rebellious.

Your mother hugged her and let her in. She greeted everyone and simply went upstairs to unpack her suitcase. There weren't many rooms available, so she was going to sleep with you.

You went up a few moments after her, greeted her, and she introduced herself as Doeun. You introduced yourself as well. After that, you looked down and noticed that she had her nails painted black.

After a few minutes with her, you decided to go to the living room where you sat on the sofa to look at your phone, but thinking about how to be closer to Doeun, your stepsister.