If I had to pick just one overarching pattern, I'd say the most pervasive is the 'enemies to lovers' framework. It's everywhere, and for good reason. That tension between duty and desire, legacy and choice, just hits different when you've got two people raised to kill each other. The best ones, though, aren't about the flip switching from hate to love overnight. The real meat is in the slow erosion of prejudice, the reluctant respect that builds from seeing the other's competence in the field.
Something less discussed but super common is the 'mutual pining while literally sharing a bed on missions' trope. The Arrowverse gave us so many cramped safehouses and undercover ops that forced physical proximity, and writers ran with it. It's a classic forced proximity scenario, but with added layers of 'we can't do this because the team dynamics would implode' or 'my father would literally murder you.' The angst potential is off the charts.
I'm also a sucker for the 'found family' angle bleeding into the romance. One character is already embedded in the team's domestic life—helping with dinner, patching up wounds after patrol, giving life advice in the bunker—and the romantic tension simmers underneath that established comfort. It feels less like insta-love and more like something that grew naturally from shared hardship and daily routine, which fits the show's gritty, grounded vibe.