Opposition implies two-sidedness. The opposite of reason is not emotion, or at least you haven’t shown us as much.

The opposite of reason would be un-reason. As an extreme example, committing a murder for a reason (pre-meditated) is different from killing someone without a reason (manslaughter). So shooting your annoying next-door neighbor is an applied reason, but accidentally hitting them with your car in a snowstorm with slippery roads has no applied reason, OR applied emotion.

So, I think you are wrong, and reason and emotion are not opposites. They are entirely separate, perhaps sometimes contradictory, tools to make decisions. Emotions can be used to make good decisions (using the feeling of guilt to recognize wrongdoing and apologizing), and reason can be used to make bad decisions (using ethnocentrism to define certain people in society as negative).

An emotion can be the driver of decision-making just as much as reason can, and the same goes for a lack of either.