Ahahaha there are SO many. Well, half of these are science fiction and fantasy tropes, but I like them specifically in the context of a romance. I like mars needs women, arranged marriage, captor/captive, angsty halfblood, secret baby, dark horse love interest (preferably the dark mage version, though dark knights are nice too), the outcast (sometimes the mutant), 98 lb. weakling, long hair, leather boots, and kilts/robes/corsets, first contact, interspecies love, lost in translation, culture clash, courtship ritual, heat cycle, soul bond, bond pet, equippable ally, color-coded for your convenience, blanket scenario, mpreg, nesting instincts, shapeshifters, dragons, marooned in space, mercenary troop, spaceship/airship, mechas/magical mechas, portal fantasy, magical testing ground, kemonomimi (aka animal accessories), love triangle ends up a threesome, and good guys turn out to be the bad guys so the MC defects from their side to the LI's side.