RectangularCircle True, but is very well know thru Asia now. Would you call a girl sister to pick her up?
Oppa vs Brother.
Citlalicue depends, maybe the girl that im trying to pick up have some weird fetish. 
But on the other note, lets say you are non korean and saying that word “oppa” to pick up a boy. Imagine how cringey you can be. Really weird to hear that coz oppa is mostly used as a endearment for young people or used literally for older types.
I can see that. So, there's no other word? Does it reeeeally translates to "brother"?
Citlalicue ye it is. because thats their culture. if you talk about korean novel then yes of course they will use oppa or hyung
dlwlrma Oh well, I gotta get used to it I guess. Thanks!!
Citlalicue by the way, what novel you read that you want to change brother to oppa?
Citlalicue well since theres no other term chinese have for brother . Maybe you can just change it to oppa when reeading. Inspect element but if ur using mobile. Goodluck!
OPPA Korean novel
Citlalicue I'm not quite sure with Chinese culture, but I know people use 大哥 and 大姐 (big brother and big sister) to refer to people a bit older than them.
dlwlrma Recently started looking into a couple of romance novels.
Beep Beep Possessed by K drama Ghost
Citlalicue That is just how you perceive brother, in China it can mean alot of things, up to and including a distant relation. Person A is a 3rd generation disciple who is a woman. Person B (Senior Brother, aka older disciple) is entertaining Person C (A visiting sect representative). Persons B and C are equal in status, and person A is of same generation, just a bit younger, therefore in that culture brother can mean anything.
adgsad Yeah, that I read in novels junior/senior sister junior/senior brother in training or battle scripts.... but, "I been in love with you brother" just sounded weird to me. I'll get used to it as I read along I suppose. 
NewCultivator Hahaha and I hate when they say it but here, I'm asking for it
- Edited
Citlalicue actually the majority of chinese males hate the word oppa as make them thinking of korean feminine men stars. some teen girls in China watch korean dramas.maybe they like it and you may find the word "oppa" in chinese female authors' works.
Confucious I can see why they hate it. 
Korean actors/singers nowadays are very feminine indeed.
Saying Oppa in English sounds ridiculously weird cause it sounds like old pa and when you. Are reading a novel and then in your head you 'say' old pa ,Oppa ,it will creep you out
Shameless7kim
Thanks for telling sharing this to us, I won't be able to remove this shit in my head now.
It could be present in the novel because the original author wrote it like that.
Gege/jiejie then