In the fall of 2019, Sarah J. Maas was sitting across from an interviewer at New York Comic Con when she said something that stuck with me. She was talking about writing A Court of Mist and Fury, the second book in her ACOTAR series, and she mentioned that the entire plot of that novel, the war, the politics, the courts, grew out of one question: what would Feyre need to go through to be ready to fall in love again?
The fantasy didn't come first. The romance didn't come first. The emotional need came first, and then both grew out of it like two branches from the same trunk.
Most writers trying to figure out how to write romantasy don't start there. They start with the world or they start with the love interest. And then they spend months trying to stitch those two halves together, wondering why the seams keep showing.
The ones who get it right tend to do something different. They find the place where the plot and the romance are the same thing.
How to Write Romantasy: Make the Romance Load-Bearing
There's a concept in architecture called a load-bearing wall. You can tear out most walls in a building and it'll stand. But take out a load-bearing wall and the whole structure collapses. That's what the romance needs to be in a romantasy novel. If you can remove the love story and the plot still works, you've written a fantasy novel with a subplot. Which is fine. But it isn't romantasy.
Look at what Carissa Broadbent does in The Serpent and the Wings of Night. Oraya enters the Kejari, a tournament to the death, and her alliance with Raihn isn't a side attraction to the competition. It is the competition. Every time they grow closer, the stakes of the tournament shift. Every time the tournament tightens, the relationship has to bend. You literally can't talk about one without talking about the other.
That's what I mean by load-bearing. The romance carries weight in the plot. The plot puts pressure on the romance. Neither is decoration.
The Scene That Does Two Things at Once
Jennifer L. Armentrout once mentioned in a newsletter that she tries to make sure no scene in her books does only one job. A conversation that reveals political information also has to shift the dynamic between the two leads. A fight sequence also has to be the moment one character realizes they'd die for the other.
I'm not sure why this works as well as it does, but I think it's because readers of romantasy aren't switching between two modes of attention. They're not reading for plot and then reading for romance. They're reading for feeling, and the feeling has to be continuous.
When you write a scene that's only plot, the emotional temperature drops. When you write a scene that's only romance, the sense of consequence disappears. The best romantasy scenes do both at once, and the reader can't separate them even if they wanted to.