My 2nd Steve/Sif story, this takes place before Avengers: Age of Ultron during the time when the Avengers were fighting against Hydra (seriously there needs to be a prequel comic or TV special showing how they decided to assemble again to fight HYDRA. I read that Thor: Ragnarok will be kind of a road movie and even though I know that's not what they mean: all I can picture is the image of Thor and the Hulk (since he will be in the movie) driving around the country in a car (I would so pay to see THAT movie!)
Sif did not know if it was because of anything wrong with her, for most of her their live even when he supported her in going into battle with him and the Warriors Three it had seemed that Thor would never return her affections. He chose to fall in love with the scientist woman that he had met in his time exiled on Midgard, by Odin's Beard he had not aged at all from when the woman's great grandfather would have been born! He had been spending a lot of time with her, especially when he chose to become a full time protector of Midgard and rejoined with the mortal allies he had in the group that were calling themselves the Avengers to fight a global organisation called Hydra (Thor had told her and the Warriors Three how disappointed he was when he found out that no the group did not have an actual Hydra).
Thor had invited her and the Warriors Three to Avengers Tower, the headquarters the mortal they called Iron Man had put together. There she took a look at some entertainment choices that the people of Midgard had. She saw some 'movie' called 300 and she had a go at an electronic game series called God of War (she had admitted to liking slaying the Gods in that game as the Olympians were jerks to them Asgardians).
Right now at the Towers' bar she was drinking her nineteenth cup of Midgardian alcohol when a tall muscular blonde man in civilian clothes, Sif known him as Steve Rogers the leader of Thor's Avengers group, apparently during Midgard's second world war he took part in a science experiment that turned him into a super soldier and had been frozen in ice until he was thawed out having survived. "Yeah I could never get drunk here anyway, the serum I took pretty much made me impossible to ever get drunk again." Steve told as she sat back down.
"So you're Sif, Thor's friend." Steve said with Sif nodding and Sif noticed that Steve was smiling as he took a look at her attire for she had come here dressed in her usual Asgardian armor. "Sorry, it's just that I like a woman that can fight." Steve said apologising but Sif could not help but smile at this, she was not so sure why but it seemed this mortal's smile was able to keep her warrior guard down.
"Yes, I have long heard that the people from the area of this world know me as their Goddess of War." Sif told him not helping but see how good looking that the Captain was, "You think we can spar, I want to see if you are as good a fighter as Thor have claimed you are." Sif asked and Steve could not help but nod at this.
Sometime later she had gotten her weapons and Steve had changed into his Captain America uniform and gotten his shield. They had sparred in a boxing ring that Tony had in the tower. The fight had lasted for a long while and Sif could not help but see how fast and good a fighter the Captain was as a mortal, especially as he fought with a shield a weapon that Sif only ever knew was something to defend with and not attack.
It was a close call but Sif just managed to get Steve's Shield thrown all the way down onto the floor outside and she was able to get him on the ground. She then helped him up and congratulated him on giving her a close and hard fought duel. "You want to go out to dinner sometime?" Steve asked and Sif had managed to mumble a yes. She later could not beleive she had found it hard to answer a mortal who she had defeated into combat. Could there be feelings for the Captain developing in her?
She had later answered the questioned for herself when she found herself charmed more and more by the Captain leading to the two unable to end their date with a kiss. Some time ago she did know why Thor could fall for a Mortal on Midgard but now she was biting her earlier thoughts for she had done the exact same thing.
It would be years before she and Steve attended Thor and Jane's wedding and they did the same for the wedding between Steve and her. Both times there were attendants from both Midgard and Asgard; both places had their own ministers present to marry the couples so it counted for both worlds. Thor and Sif knew that that the time to spend with their spouses would not be that long to them but they knew that the time they would make due of the time that they did have.
It would be decades when Steve did succumbed to death in a battle with the Nine Realms at stake, so with her beloved Captain in Valhalla where she hoped to rejoin him someday she would take care of their Midgardian/Asgardian hybrid children with stories of the times she had spent with their father, including their honeymoon which was spent fighting off a Kree Invasion of Asgard...
I read that in a deleted scene for Age of Ultron Thor said the Greek gods were just myths but the poke was too good to pass up and I think they might prove it wrong (since I would like to see Hercules in the MCU).