Enemies-to-Lovers
A trope in fiction where the individuals involved start off their relationship as enemies and then eventually turn into Lovers. They may be hostile towards each other at first, or have just met each other on unfortunate circumstances.
"Zuko was a villain in ATLA and Katara was a protagonist, if they ended up together they could have been an iconic Enemies-to-Lovers ship."
Friends to Enemies to Lovers
A common fiction trope in which two characters, which were previously friends, fall out through an event/situation that causes them to hate one another. They have a rocky relationship for some of the trope, eventually find their way back to each other and fall in love.
Friends to enemies to lovers can be seen in many YA books, animes and TV shows.