In the anime series Haruka and Michiru (Sailors Uranus and Neptune) are a couple confirmed by the author Naoko Takeuchi
Takeuchi has openly admitted they are a romantic couple, and their voice actresses were instructed to play the characters "as if they are a married romantic couple."
Source: List of Sailor Moon S episodes
In the first season we learn that the Sailor Senshi (or at least the first five) whom we see are reincarnations of their past selves from the Silver Millennium. They were friends and bodyguards of Usagi's past self, Serenity, as well as princesses of their representative planets.
I am wondering, however, if Haruka and Michiru are too reincarnations of their former selves, princesses of Uranus and Neptune, and if so, whether the Princesses Uranus and Neptune were a couple as well?