The Past

As the story dictates, 1000 years ago was the Silver Millenium on the Moon. It was a joyous time for everyone. The ruler of the Moon Kingdom was Queen Serenity and she had one daughter, Princess Serenity/Serena. Princess Serenity had fallen in love with a human Prince from Earth, Prince Endymion/Darien.

Unfortunately a conflict had arisen between Earth and the Moon and the Earthlings were not trusted (The Moon Kingdom thought the Earthlings wanted to be able to live for 1000 years as they did). This did not help the Prince and Princess's relationship. They would often have to meet secretly but their connection grew more and more every time they met.

One night, before the battle against Earth would begin, Serenity/Serena gave her Star Locket to Endymion/Darien to make sure she would never forget him, and what they had together.

Finally the time came when the Earthlings attacked (With Queen Beryl leading them). The Prince fought on the side of the Moon to protect his love. This fight came to a bitter end for the Prince and the Princess were both killed. Fortunately Queen Serenity was able to destroy the enemy and send the people of the Moon to a new life on future Earth.

The Present I

The romance between Serena/Usagi and Darien/Mamoru has been a very jumpy one since the start of the show. The two didn't really hit it off that well till much later in the first season of Sailor Moon, when the past is brought to light. Throughout the first season we get hints as to who is who and how the past ties into the story but never enough to make a clear decision. The romance really begins to show at the beginning of Zoisite's quest to get the Rainbow Crystals and the Silver Crystal. This is when Darien/Mamoru first discovers he is Tuxedo Mask/Kamen and starts to understand the dreams he is having. In one of the episodes an artist asks to have Darien and Serena be her models. In her studio Serena discovers a picture and shows it to Darien, who realizes that it is a scene from his own dreams. Him, giving the Moon Princess the Locket from so long ago.

Darien/Mamoru continues to get the visions till the Moon Princess is discovered. In this episode the Moon Princess is reveled and the two lost lovers from long ago are freed. Darien/Mamoru is captured by Beryl and pitted against the Scouts/Senshi, but his love breaks through in the end and he always manages to not destroy Sailor Moon, but save her. He is finally totally brainwashed by Beryl.

Darien/Mamoru attacks Sailor Moon in the form of Prince Endymion/Darien, but is freed of the evil spell by the love deep inside opened by the Moon Locket song, which only played for the two lovers destined to be together.

The Presnt II

In Sailor Moon R from the first episode that Rini/Chibi-Usa arrives, Serena/Usagi and Darien/Mamoru's relationship falls on some hard times. It all begins with a nightmare that Darien/Mamoru gets one night about Serena/Usagi in the future. It warns him to keep away from her or she will die. The next day, he breaks up with her and she is heart broken. Later on, Serena/Usagi gets the same sort of dream. Being the felling sharing girl she is, she tells Darien Mamoru about the dream she had. They talk and realize it was all a trick and get back together. In Sailor Moon R the Movie the romance is once again threatened, this time by one of Mamoru's old friends, one he had met as a young child when he was in hospital, Fiole. Fiole will not let anyone stand in his way to repay the humans for having left Mamoru alone for so many years.
He does not realize the important element that Usagi plays in his life now. Eventually Mamoru comes to Usagi's rescue by attacking Fiole. Fiole does not understand why he would want to protect such a deceiving girl and Mamoru explains to his friend what Usagi means to him. Usagi uses the power of the Silver Crystal to break the spell cast over Fiole, and to save her friends. The use of the crystal would normally kill her (as it did her mother) but Fiole, a true friends helps her by giving Mamoru the nectar of the flower of life and his kiss revives her.

The Present III

In Sailor Moon S Usagi and Mamoru's relationship does not take precedence over anything else in the story. The two are simply going out the way it was meant to be. They see each other and love each other, as a couple should. In Sailor Moon S the Movie, Usagi and Mamoru's relationship is put back into the light when Luna asks Usagi about love, how love works and what the feelings mean. Usagi explains with Mamoru as her example. Throughout the rest of the series the relationship between Usagi and Mamoru comes up briefly but never more then is needed. It is known that they date and love each other very much and that is how it remains.

The End...

As the Manga dictates, the Sailor Moon Romance Saga ends with the marriage of Usagi and Mamoru. These two star-crossed lovers from the past finish what could not be done on the Moon Kingdom 1000 years ago. The wedding turns out to be the be all and end all of the Usagi/Mamoru relationship in Sailor Moon, at least in the Manga. In the Anime, the series and romance ends a little differently, with no creation of Crystal Tokyo and no wedding, but just two lovers, kissing under the full moon.