약자가 · 약자를
the weak, the vulnerable, underdog
Example
강자보다 약자의 편에 서는 사람이 되고 싶어요.
I want to be someone who takes the side of the weak rather than the strong.
Word parts
약 weak+자 person
Literally 'weak person'.
Good to know
Homonym: 약자 can also mean an abbreviation; context makes it clear.