Sikeurit Gadeun2010

[In Korean forms of address, everyone is like family, and "oppa" signifies an older brother - not necessarily a blood relative - who looks out for a younger sister. Joo Won's jealousy is tweaked when Ra Im calls Oska her "oppa," designating him as an older male peer who looks out for her]

Kim Joo Won:
Starting today, your oppa is me.

Gil Ra Im:
What?

Kim Joo Won:
From now on, if you call anyone else oppa, I shall consider it cheating.