Disclaimer: I own none of the characters from the Buffy verse or the Marvel Avengers Movie verse...
Agent Coulson calmly shut the glass doors of the defunct gas station that was Jane's current laboratory. "SHIELD has a perimeter around the town. Now, explain."
Darcy stood near the back of the room, leaning against a desk with her arms crossed across her chest. "And, what's to stop the rumors of me being a Slayer among the agents?"
Coulson gave a small smirk. "The agents who heard you know not to say a word. If they do, they'll have a lovely life at McMurdo Station."
Jane went wide eyed. "You can do that?"
Coulson nodded. "Of course." Turning to Darcy, he raised an eyebrow. "Well?"
"Fine," Darcy sighed. "This does not leave this room. It is not to go into any databases or reports. The only person who can be told any of this is your Director Fury. My Council contact told me that you can tell him, whoever he is, everything, as long as you are one hundred percent positive it isn't overheard or recorded."
Nodding, Coulson replied. "He's the head of SHIELD. Considering what I know about the Council, I agree. I'm more interested in how you came to be here, with Jane as your Watcher."
"I want to know what is going on!" Erik exclaimed, throwing his arms into the air.
"Okay, quick version," Darcy replied, nodding and walking over to a large cabinet. Pulling out a length of rebar, she handed it to Erik. "Bend it."
"It's rebar," Erik pointed out.
Darcy rolled her eyes. "Just bend it."
As Erik strained to bend the length of metal, Darcy started her explanation. "The world is full of supernatural things. Ghosts, demons, all that. Most are peaceful. Some aren't. In the mists of time, Slayers were created. Girls with supernatural gifts of speed, strength, etc. We fight the oogie-boogies and keep humanity safe. The Council is our support network."
Erik snorted. "You expect me to believe this crap?"
Darcy grinned and took back the rebar. "You couldn't bend it." Then, with no effort, she bent the straight length of metal into a circle.
"What? But? What?" Erik sputtered.
"We'll explain it in more depth later," Jane said, patting Erik on the shoulder as she passed him a beer.
"Now that the background is out of the way?" Coulson prodded.
Darcy nodded. "Right. I was at school, looking for an easy way to get my science credits, and saw Jane's internship. Astrophysicist trying to prove wormholes exist? Yeah, possible bad news. So, I contacted the Council. They looked into it and thought she had a good chance of succeeding. So, I was asked to apply for the internship. Luckily, I got it."
"Why would wormholes be bad?" Erik asked after taking a pull from his second beer.
"As Thor proved, there are many realms, worlds, dimensions, whatever you want to call them," Darcy pointed out. "Not all are nice places. In fact, there are locations on the Earth where the border is thin. And, on the other side? We consider them hell dimensions. The Council watches those areas closely.
"So, I'm here to make sure that Jane doesn't open a portal to a bad area of the universe. If she does, I'll either help close it, or try to hold off anything that comes out until back-up arrives."
Looking pensive, Coulson nodded. "That makes sense."
"Now what?" Jane asked.
"You and Doctor Selving come work for SHIELD, where you'll have a building full of agents in the background to help if something goes wrong." Coulson held out a folder.
Jane glared."And, Darcy?"
"I'm going to contact the Council about becoming her Watcher."
"Hey! What for?" Darcy exclaimed.
Coulson gave a mild glare. "Now that I know you're a Slayer, your behavioral pattern around town makes sense. Luckily, there can't be many demons in this town."
"You'd be surprised," Jane muttered with a sad look.
Darcy gave Jane a one armed hug. "It's okay, Jane. I made the kitten poker circuit leave town." Turning to Coulson, she glared. "First off, I'm fine here. And, if I don't want you?"
"Fine here won't cut it in New York. And, You don't get access to SHIELD headquarters," Coulson said with a smirk.
"That's blackmail," Darcy glared. "And, I'm not an active slayer."
"I'm not surprised SHIELD would resort to blackmail," Erik snorted.
Jane sighed. "I'm going to put him to bed and let you two argue," she said as she grabbed the folder from Coulson and led Erik from the room.
"You aren't going to back down, are you?" Darcy said with a groan.
Coulson didn't reply, just stared with a raised eyebrow.
Darcy threw her arms into the air. "Fine! Whatever! I still work with Jane, I don't patrol unless the Council needs it. I'm only available as back-up or in emergencies."
Coulson nodded. "That's doable. You keep in reasonable shape, just in case. You make weekly, face to face, reports to my office on Jane's progress. During that time, you'll also give me a personal weekly update. Also, you'll listen to my suggestions with an open mind."
Taking a deep breath, Darcy nodded. "I can work with that. You'll have to do the Watcher training before it's official though." The last was said with a devilish grin. "Don't worry, there's a condensed version that takes three days. Of course, it's sixteen hours each day. You'll love it. It'll be fun!"
A few months later...
Parking his sedan in the spot designated for visitors, Agent Phil Coulson of SHIELD got out of his vehicle and locked the door. Striding to the front of the mansion nearby, he used the knocker on the door.
The door opened a few moments later to reveal a teenage girl in pigtails, jeans, and a ratty t-shirt. After looking Coulson over, she said, "If that was tweed, you would be so old school. You must be here for the Watcher crash course."
Coulson nodded. "Phil Coulson."
"Right," the girl said with a shrug. Holding the door open, she motioned him inside. "First lesson," the girl continued as Coulson entered the building. "Never verbally invite anyone into your residence."
"Noted," Coulson replied.
"Oh, we're going to love you," the girl smirked as she closed the door.
This is actually two ideas I had... 1) Darcy explains about Slayers and 2) Coulson goes to Watcher school... But, the Coulson in Watcher school petered out... So, I turned it into a coda to this story.