This is information on the relationship between Duo and Hilde. Certain areas will be based soley on my personal opinion, but I’ll try to keep it as impartial as I can. Spoilers are all over the place.
History:
Duo and Hilde met when Hilde approached Duo to invite him to join Oz. He came to the “initiation party” (for lack of a better term) and ended up attacking the group. He fled in his Gundam and Hilde went after him. It was during their brief battle that Duo discovered Hilde’s real reasons for joining Oz. She really thought she was doing the right thing and only wanted to protect the colonies. Duo tried to convince her that they were on the same side, but she refused to listen (at first).
Later, Duo is taken captive and Hilde goes in to question him. He explains that he’s fighting for the colonies as well, and that Oz is the real enemy. After considering his words, Hilde decides to help Duo to escape and destroy the moon base.
A few episodes later, Duo and Hilde are seen on the colony, living together and helping each other out until things calm down. Duo is forced to try out the Zero System by the Oz soldier Trant who has been using the Wing Zero. Because of the Zero System, Duo sees strange visions of himself destroying the colony. The last image he sees before “waking up” screaming was Hilde being killed.
As the episodes pass, Duo remains in Hilde’s company. Hilde takes Duo to the circus to cheer him up and they see Trowa, whom the others believed to be dead. Duo questioned him about the whereabouts of the other Gundam pilots, but Trowa had lost his memory. Duo returns to Hilde’s home.
After people discovered that Duo was a Gundam pilot, he knew that his presence posed a threat to Hilde and her home. He decided to leave for space and Hilde asked to go with him. He quickly told her no and instructed her to stay in the safety of her home. As he left, they shared a bittersweet goodbye (Hilde watched him leave from the roof with teary eyes).
Later, Hilde is seen again by herself, sneaking aboard Libra and stealing important data. She has a brief encounter with Relena Peacecraft before leaving for Peacemillion. On her way, she is attacked by two powerful, advanced mobile suits. She fights her way forward and manages to make a plea of help over the radio system. Duo hears this and goes to find her. Duo easily destroys the attacking mobile suits and asks Hilde if she’s ok. She shows him the data disc and tells him that she got it for him. He’s very upset and angry because she put herself in danger when he had specifically asked her not to, but concern and worry are apparent in his face and voice. He speaks with Hilde briefly before taking her to the medical area of the Peacemillion. She tells him that she spoke with Relena and Duo informs Heero of the news. Hilde is not seen throughout the rest of the anime series (actually, there were only about two episodes after that).
In Endless Waltz, we see that Duo has been with Hilde since the war and they have opened a scrap yard together (which was a hobby they conveniently shared). After the events of Endless Waltz, Duo is seen talking to Quatre about how good it is to have a place to call home, then he is immediately seen returning to Hilde.
Why they make a good couple:
It’s pretty obvious that these two get along perfectly. They enjoy most of the same things and complement each other well. They’re both friendly and honest. They both love to have fun. I can see these two as the type to go out partying together, but have just as much fun horse-playing around the house or watching movies. These two could make any situation enjoyable. A lot of people say Hilde can’t understand Duo because he’s had such a horrible life, but we can’t really say that. None of us know the details behind Hilde’s past. Her parents are never seen or mentioned in the series at all. What if she was an orphan all her life just like Duo? We don’t know what happened to her, so we can’t say that she’s had it good. So what if she’s cheerful? Duo is cheerful too, yet he’s had a lot of bad things happen to him. She may be covering up her pain just like he does. The point is that WE DON’T KNOW.
My Speculations On….
Domestic Duties: In my opinion, these two would probably share the household chores and cooking. They share everything else, don’t they? They share the scrap yard, I know, which means they both bring in equal income (unless one of them does odd jobs on the side).
Children: These two would definitely have children, but I believe they’d wait a great number of years before they do. Why? Because they’re fun-lovers. They enjoy their freedom and like to go out and party. After they’re older and settle down, I’m sure they’ll want to have little Duos and Hildes running around.
Sex: This is a little tricky because people can fool you. From what I’ve seen, however, they would probably be very experimental and make sure to try everything. Whatever they do, they’d have fun just trying it out.