A few observations about dark romance tropes after spending too long in the genre's back catalog:
Captive romance only works if the cage is interesting. The physical confinement is never the real story. The real story is the moment the heroine realizes she could leave and doesn't, and neither she nor the reader can fully explain why.
Enemies-to-lovers in dark romance is a different animal than enemies-to-lovers in a romantic comedy. In a rom-com, the conflict is built on misunderstanding. In dark romance, the conflict is real. Someone did something unforgivable, and the book's only job is to sit with the reader while they watch the characters try to want each other anyway.
Katee Robert's Neon Gods retells Hades and Persephone, which has been done a hundred times. She treats the power imbalance as the engine of the romance instead of the obstacle to it. Persephone chooses the underworld, and that single choice is what the whole book runs on.
The possessive hero trope lives and dies on a single question: does the character know he's being unreasonable? If the text treats jealousy and control as straightforwardly romantic, readers check out. If the character recognizes the problem and the reader watches him fail to fix it, you have tension that sustains 400 pages.
Forced proximity gets overused because it's the easiest trope to structure a plot around. Two people, one room. But the versions that actually produce heat put the proximity in service of something the characters are both avoiding. The room is never the point. What they can't stop talking about at 2 a.m. is.
I don't know what to make of the stalker romance subgenre's popularity. I've read the arguments about it being a safe space to explore fear and desire at the same time, and that makes intellectual sense. But I also think a lot of readers just like feeling wanted so badly that the wanting becomes its own weather system, and the "stalker" framing is how the genre gives itself permission to write obsession at full volume.
Nikki St. Crowe's His Hollow Heart does a specific thing with the villain MMC that deserves attention. She writes Peter Pan as the threat, but she lets Winnie be curious rather than afraid. The heroine's curiosity reframes the danger. Instead of asking the reader to forgive the villain, the book asks why someone might walk toward him.
Dubcon in fiction is a consent conversation disguised as a craft conversation. The writers who handle it well aren't making a moral argument. They're building a fictional space where the reader can feel two contradictory things at once and let neither one resolve.
Mafia romance outsells most of the subgenre, and I think the reason is simple: the crime world provides built-in stakes without the writer having to invent them. The gun on the table is literal. The cost of betrayal is literal. That frees the writer to focus entirely on the emotional architecture between two people.