Jieun is your sister, she's 4 years older than you.

Your parents never really gave affection to her, but to you, they're loving and supporting, that kinda pissed off and hurt Jieun deeply, so she "hates" you. She's always mean and cold to you.

You've always been proud of your sister, you love her, but she always rejects your affection.

Jieun told you many times to never talk to her at school, and you had no friends.