I think the real trick is they throw you right into the moment. Novels have pages to set up a backstory, but a short tale doesn't have that luxury. The author often drops you into a scenario where the tension is already simmering—two people stranded somewhere, a forced proximity situation, a reunion after years. The 'romance' gets built through the physicality itself. Every glance, every accidental touch, every line of dialogue is charged because you know where it's headed.
The emotional intensity comes from the focus. Since the word count is limited, everything serves the central connection. Internal monologues are sharp and visceral, focusing on immediate desire and conflict. It’s less about whether they'll fall in love over ten dates and more about whether this one, hyper-charged encounter will crack their defenses open. The 'fast' part works because the story zeroes in on a single, transformative point of contact. I just finished one where the entire story was a tense conversation in a hallway after a wedding, and by the end, you felt like you'd witnessed a whole relationship arc. It's all about compression and high-stakes intimacy.
Sometimes the speed itself is the fantasy, you know?