foil; person who makes someone else look better
Refers to a person whose role is to make another person stand out or appear more attractive by comparison. Often used in social, entertainment, or comedic contexts.
He always ends up playing the foil to his friend.
お笑いコンビでは、ボケと引き立て役のバランスが大事だ。
In a comedy duo, the balance between the funny man and the straight man is important.