Enemies-to-lovers is my favourite romantic trope. There’s nothing more satisfying than reading about/watching two characters who are polar opposites* reluctantly fall for each other. Yet writing this trope can be tricky – you want to make their love seem improbable without making it impossible.
* There are exceptions that I don’t believe are romantic and this can be summed up as any potential relationship that has an unequal power balance (eg Nazi-Jew or slave owner-slave.)
Oil and Water
Make your characters as different as you can: the jock and the geek, the con and the cop, the god and the mortal; and so on. Yet despite all their differences, they need something in their pasts that means they’ll eventually be able to relate to one another. You can hint at this through internal dialogue but don’t let them mention it out loud.
Have something happen that forces your characters together, otherwise you have no story. Whether it’s a fight against the elements or against a bigger enemy, what they’re facing means they have to work together in order to survive. Though not before they have several arguments, of course!
Every little thing one character does annoys the other no end, and vice versa. They snore or chew their nails or twist their hair. These habits are a source for further fights but should also show that the characters are paying attention to each other.
Both characters ought to have a pained moment where they realise how much they’re noticing about the other. Extra cookies if they have a moment where they actually manage to work together without griping and then pull back in shock.
Rocky Common Ground
This is where your characters know they have to work together to solve the problem but don’t like it. Yet the moments of genuine partnership are increasing. Let them talk and start to get to know one another. One or both may believe this glimmer of friendship is fake/contrived.
Doubt doesn’t stop them noticing more and more. Add offhand touches and sideways glances. Or even deep, longing stares. Erode their reasons for not getting together.
One character mentions someone they know of the opposite sex. The other gets flustered, because they want to know who this person is – and how important they are. Yet they can’t come out and ask as that shows the information matters. Let this situation simmer; maybe have this third wheel mentioned often and the character continue to be tied up in knots. The first character can either remain obvious or realise what’s going on and use it.
The sexual tension goes off the boil in the opposite direction by your characters having a physical fight. This can be anything from a shove to a full on drag down.
Have the characters end the fight without no clear winner in order to maintain the power balance. Or, if one must win, have them do it by cheating. You can certainly let this expand into angry sex. I loves me some angry sex.
Solid Common Ground
Let your characters take care of each other in the aftermath. If their issues weren’t aired during the fight, do it now. You want them to move to being friends now. Let them talk and find something they have in common other than the need to survive – this can be anything from a love of kittens to flunking the same class or maybe they were once in the same place at the same time but never met. They should acknowledge out loud that they need each other to win against the odds.
Your characters are back to work… and back to making physical and eye contact, but this no longer by accident. Fingers brush and gazes long and sooner or later, they give into the mounting desire. If you don’t want to write a sex scene, then don;’t force yourself, but your readers need to know that line’s been crossed. If nothing else, let them have a nice little cuddle afterwards as they go to sleep in each other’s arms.
Back Off Yer Bastard Or I’ll Break Yer Legs
So now your characters are lovers! Yet they can’t celebrate just yet as whatever brought them together in the first place still needs dealing with. If it’s an antagonist, well they probably thought they were going to deal with one or the other. That they’re fighting as one? Oh, boy.
After all they’ve been through neither wants to lose now, so let them fight for, and protect, one another. This is where both are going to stand there ground and say to the Big Bad “YOU SHALL NOT PASS!” Maybe they don’t get out without being injured, but they ought to emerge victorious and more or less in one piece.
Big Damn Heroes
The day is saved! Voldemort is dead, the Empire is defeated, and Winter is over. Now is the time for celebrations, whether that’s them being awarded something or riding off together into the sunset. Let them gaze into each other’s eyes or snuggle down together. Or both – both is good.
In short, let them get gooey and romantic. Have them recount the first time they saw each other and laugh about how ridiculous they were. Most importantly, let them declare their love. Fade.