A/N: In some of these, I'm leaving out T'Challa due to cultural differences and Peter due to his age.

...

Clint Barton/ Hawkeye

You were taking a walk in Central Park with Clint, your hands intertwined. Clint was telling you stories from his past.

"... and then we pushed him outside totally naked and locked him out!" You burst out laughing at this.

"Oh, that reminds me," he said letting go of your hand and started to fish through his pockets. He smiled when he found what he was looking for and handed you a key attached to an arrow keychain.

"What's this?"

"It's a key," he grinned.

"I can see that. What's it for?"

"My apartment. I like having you around and I want you to have a key to my place." Your eyes widened a moment before you smiled. You put the key in your purse and started dragging him away.

"Where are we going?"

"Someplace that cuts keys. I can't let you give me a key to your place and not let you have one for mine," you smiled.

...

Tony Stark/ Iron Man

This had been something you had wanted to do for a while, but to be honest, you were a little nervous about it. One night, Tony had taken you out to a fancy dinner. Throughout the meal, he had noticed you looking a little fidgety.

"You okay babydoll? You seem a little twitchy." You took a deep breath in. It was now or never.

"Tony... there's something I want to give to you," you said, reaching into your purse. You pulled out two keys attached to a rainbow coloured keychain.

"What're they for?"

"One's for my apartment, the other... is for my studio." You had never given anyone a spare key to your studio before so this was a big step for you. To your relief, Tony smiled and put them in his pocket before pulling something out.

"This is perfect, because I want to give you this." Tony handed you an access card with your name on it.

"This'll give you access into the Tower at any time. All we need to do is get your beautiful picture taken and you'll be all set," he beamed.

...

Pietro Maximoff/ Quick Silver

You were just getting back from a date with Pietro. You had a key cut for him but you hadn't given it to him yet.

"Hey, Zippy?"

"Yes, Y/N?"

"I had this new key cut today. Would you mind seeing if it works?" you asked, handing him the key that was on a keychain that had a little light-blue sneaker on it.

"Okay..." he said, taking in the mischievous twinkle in your eye. Pietro put the key in the door and twisted it, making it unlock.

"It works fine, Princezná."

"Oh, good. Since it works, why don't you hold onto that one?" you smiled. Pietro was a little confused at first.

"Are... are you giving me a key to your apartment?" he asked. Grinning, you nodded your head and he beamed at you, wrapping his arms around your waist.

"I shall return the favour as soon as I can."

...

Thor Odinson

Whenever Thor was in Midgard, he usually stayed at the Tower, but since he'd been dating you, you'd been letting him stay at you place. Sometimes, this caused problems because while he was waiting for you to get home, he'd stay outside your door and interacted with your neighbours. Normally they didn't mind your weirdness but Thor's loud and somewhat unusual nature was starting to get to them so they were starting to complain. One day you just handed him a spare key, complete with a little hammer keychain.

"What is this?" he asked, looking at the object in his hand. He knew it was a key of some sort but what it was for, he didn't know.

"It's a key to my apartment. It's so you can come in and make yourself comfortable without waiting outside my door." Thor smiled and kissed you.

"Then I shall treasure it, Lady Y/N."

...

Sam Wilson/ Falcon

You and Sam were taking a leisurely stroll through the streets of New York. Sam's hand slid into the back pocket of your jeans, which was not unusual by this point. After a while, he put his hand around your waist and as you were walking, you noticed something poking your butt. Putting your hand in your pocket, you felt an unusual shape. You took hold of it and pulled it out, seeing it was a key, you looked at Sam, who was grinning.

"Explain," you demanded.

"It's a key to my place," he said proudly. "I want you to have it." You were slightly stunned at first but then you smiled and rummaged through your handbag.

"I have one for you too," you beamed, handing it to him. He smiled when he saw the little falcon keychain you had attached to it.

...

Natasha Romanoff/ Black Widow

You were spending your day off with Natasha at your place. You were just watching some movies with her, just being content with her company.

"This is nice," she smiled, loving the way your fingers were combing through her red locks. "We should do this more often." You suddenly remembered something.

"Nat, there's something that I want to give to you," you said, getting off the couch. You looked around in a drawer before finding it.

"I... want to give you a key to my apartment." You handed her the key, making her smile when she saw the keychain, which was a black widow spider encased in plastic.

"Y/N... are you sure?" You nodded.

"I am. We've been seeing each other for a while now, and I've never given anyone a key before. I love you Natasha and I trust you." Natasha beamed at your words and kissed you deeply.

...

Bucky Barnes/ The Winter Soldier

You had been wanting to give Bucky a key for a while, now. Bucky had come to pick you up for a date and you invited him inside and made him sit on the couch.

"Wait here and close your eyes." Bucky did as he was told. He could hear you moving around before he felt you grab his right hand and press something into his palm.

"Okay... open them." Bucky opened his eyes to see a key attached to a keychain with a little toy soldier on it. He smiled, stood up and hugged you.

"Thank you," he said, kissing your temple.

..

Scott Lang/ Ant-Man

You and Scott had already decided on exchanging keys. The next time you saw each other, you already had them made up. You showed Scott his, (complete with and Atom Ant keychain) and he reached for it, but you pulled away at the last second.

"I have one rule; you can't come over whenever you feel like it."

"Oh yeah? Well, you can't come over you feel like it 'cause... oh, who am I kidding? The guys'll love a pretty girl coming over, especially Luis."

"Come on, Scott, I have an impressionable young daughter to think about."

"Yeah, I get it," he sighed, handing you his key.

...

Steve Rogers/ Captain America

Steve wasn't so sure about moving in with you. He loved you, but he was still very old fashioned but when you suggested exchanging keys, he accepted. It was like a small adjustment to being a couple in the twenty-first century. It was a simple gesture but it was sweet nonetheless.

...

Loki Laufeyson

Loki had just walked you home after your date and you invited him inside.

"Loki... I have something for you," you said.

"What is it, my love?" You walked over to a cabinet and opened one of the drawers, taking out a key with a little snowflake keychain and handed to him.

"Here... it's a key for my apartment," you told him. Loki looked astonished.

"You really trust me with this?"

"Of course, Loki. I love you." Loki pulled you into a loving embrace.

"I promise you I will not abuse this gift you have given me."

...

Wanda Maximoff/ Scarlet Witch

Wanda was meeting up with you for a date. She came up to you with a big smile on her face.

"I have a surprise for you. Close your eyes and hold out your hand." You did as you were told and felt her put something into it.

"Open them," she told you. Opening your eyes, you saw a key that was attached to a keychain that had a tiny little witch doll, wearing a red dress and hat.

"It's a key to my apartment!" she said excitedly. You beamed at her and hugged her tightly.

"That settles it. I've been wanting to give one to you for a while but I was scared I'd be rushing things. Come on; let's go find a place that cuts keys so I can give one to you."

...

Bruce Banner/ Hulk

Bruce was slightly worried about moving in with you in case but when you suggested swapping keys, he was okay with it. Bruce gave you a key-card that would give you access to the Tower and you gave him a key to your apartment along with a little double helix keychain.