Antagonist or villain
The enemy of the story is typically referred to as the antagonist. This character opposes the protagonist and creates conflict within the narrative.
The main character is the protagonist, and his/her enemy is the antagonist.
protagonist
A racoon's main enemy would be a wolf.
'enemy'
The Covenant are the main enemy of the Halo Franchise.
the cilmax of the enemy story is when the messenger come to Sadao's house
The most important being in your story is the main character -- it doesn't have to be a human!
The main character's (the sniper) motive is to kill the enemy sniper on the rooftop of the building across the street.
the main event is what the book mainly talking about
Germany was Britain's main enemy.
The main enemy of the Greeks is Persia.