Korea~

For a girl you use:
Oppa (오빠) - For older Brother or Friend (oh-pa)
Unni (언니) - For older Sister or Friend (oo-ni)
Dongseng (동생) - For anyone younger than you for both genders

For a guy you use:
Hyung (형) - For older Brother or Friend (he-y-ung)
Noona (누나) - For older Sister or Friend (N-oo-na)
Dongseng - For anyone younger than you for both genders

They are pronounced very similar how it is written out