The person doesn’t have to be good themselves, but they can bring the good out of others. The word doesn’t have to be an english word, I just want to know if such a word exists.
Ex. Beauty with the Beast. Durga with Asura(Asura’s Wrath, not the religious scripture). The 3 ghosts in the Christmas Story with Scrooge.
One would most likely use “complements.”
By the way, in literature, a “foil” is a character that complements another, such as in the case of Sancho and Don Quixote.