The Worst of Enemies Become the Best of Friends is a plot device that is used in romances (I guess?). The plot devices work like this, there are two main characters in the story, the lovers. When they first meet they soon become enemies and hate each other.
As the story progresses, the two soon grow closer too each other after some sorta stupid event in the middle of the story, I guess?
And soon they are in love with each other and kiss like every fucking romance out there on Earth and probably the universe.