Building the A/B/O system with internal consistency
The omegaverse's A/B/O system is a complete speculative biology with social implications that extend to every aspect of the world: professional hierarchy, family structure, legal rights, healthcare, education. Building this system with internal consistency requires deciding what the biological designations actually mean — what percentage of the population is alpha, beta, omega? Are designations apparent at birth or emerge at puberty? Can they be suppressed or medically managed? — and then working through the social consequences of those decisions. The worldbuilding that is consistent in the background, that the reader can feel even when the narrative is focused on the romantic plot, gives the omegaverse the feeling of a genuinely imagined world rather than a set of romantic conventions dressed up as worldbuilding.