But, curiously enough, i did some googling again and this is what i've found:
Oppa (오빠) means "older brother" but it's also commonly used by females towards older male friends. Hyung (형) is used by males towards older male figures. The females call unni (언니) that is for a female to call her older sister. And nuna (누나) is what a male would call his older sister. And a younger brother or sister called dongsaeng (동생). Both males and females using that word.
But when I talked about this "Oppa" word to my K-friends, they were totally not agree with my "great feeling" that i have about that "Oppa" word T.T Some even said to me that it’s not really right nowadays to use the word "Oppa"
"About Oppa...Originally, you call your brother "Oppa". but these days, when you get to know an older guy you can call him "Oppa". But some people don't like it, old people don't like it, and some young guys don't like it, because the word "Oppa" became so cheap. "Oppa" is quite common.."
And this last one was half of my conversation with my other K-friend:
ME: "Is that true that people say nowadays the word "Oppa" is often being used in Night Club and some other places like that?"
HIM: "Oh you know that? That is WHY i don't like the word "Oppa" that much. It became cheap. Using by some women in entertainment business, like: noraebang, and gayojujum, and room - night club.."
ME: "How about chagi?"
HIM: "Chagi is still good. You can use it ^^"
So, that was also why my friend told me that she called her bf long time ago with Chagi (자기) instead of Oppa (오빠) and also explained why he wasn't too comfy when she still called him "Oppa" long time ago, and asked her to change it into "자기"
Just chatted with someone and he said Korean guys are still like to be called "오빠" haha~~ and he was laughing when i said about that word 오빠 that is now used commonly in nightclubs..he said yes but anyway..I agree with him that the word sounds lovely~! "오빠"