(A/N- Is it weird I got this idea while watching Gravity Falls? No? Okay good. I never liked the homunculi, they're all murderous jerks. And, SPOILER WARNING! They killed Hughes.
Those butts.)

***Al's P.O.V.***
(Y/n) had started acting a little differently a few months ago. She was a lot more extraverted than she usually acted. I guess it was just her opening up to brother and I more. I mean, I love (Y/n) however she is, but it was nice to have her less reserved, and more talkative. She told us what she was thinking rather than keeping it to herself.
So I decided that I would do the same. I was going to stop being shy, and tell her I loved her.
When I confessed, she tried to put it as delicately as possible.
"I, I only love you as a friend. I'm sorry, but, you don't have a body and, I just would like a hand to hold and," she had trailed off.
I had looked down at the ground sadly, saying, "It's okay. I understand."
But no matter how much I tried to convince myself that she could never be mine, I couldn't stop thinking about her. She was just so beautiful, smart, funny, and kind. And she was skilled with alchemy, even though she got that way through the same taboo as us, trying to bring back her father. She had lost her left arm in the process.
About a month before my confession, brother had noticed that someone was following us. They were heavily cloaked, and whenever we saw them, they had a mask covering their face and a hood over their head. They were trying to hide some distinctive feature.
"Do you think it's the homunculi? They could be trying to hide their tattoo," I had suggested to Ed and (Y/n).
"That seems like a possibility. They've been following us since a few towns back though. Usually they're a bit more subtle," Edward thought aloud.
"They could be trying to show that they know what we're doing. They might want to show off their power," (Y/n) said.
"We can't really do anything about it, anyways. All we can do is keep an eye on them for now," Ed concluded.
To make matters worse, I was fairly certain I had seen them listening in on my confession to (Y/n).
Now we were all sitting at a train station, resting from our travels. We had accidentally missed our train due to brother oversleeping... again.
"I told you you shouldn't stay up that late. But did you listen? No. No you didn't," (Y/n) said angrily.
"Well sorry for trying to get more research done on the Philosopher's Stone!" Edward shouted back.
"Brother, (Y/n), please don't fight. Fighting won't solve anything now," I pleaded.
They both glared daggers at me, and I shrunk back a little.
They both continued shouting at each other, and I sighed. Arguing was something (Y/n) had acquired a few months ago as well.
Footsteps sounded in the air as the yelling continued, but I seemed to be the only one who noticed them. I looked around for the sound's origin, and that's when I saw them.
The cloaked figure, the one that had been following us for a while, was standing about thirty feet away. Their face was covered as usual, a signature mask hiding it. They were staring directly at me, as though trying to show that they knew I saw them. They stayed frozen for a few seconds, eyes locked with mine, before they started running. They were running directly towards us. Directly towards (Y/n).
"(Y/n), watch out!" I shouted.
She turned around just in time to get slugged in the face by the stranger. She fell limp to the ground.
"(Y/n)!" Brother shouted, clapping his hands together and touching his automail arm. A blade formed out of the metal.
"Do not interfere, I don't want to hurt you," the voice sounded as though it wasn't used to talking as it was doing. They were trying to disguise their voice, trying to make it sound different.
"I won't let you hurt her! She might not feel the same, but she's the only girl I've ever loved!" I said, stepping between the cloaked figure and Ed and (Y/n).
"Let her defend herself. She has an automail left arm, let her clap and change it to a blade. Or has she not been able to do alchemy for the past few months?"
Wait a minute, this stranger had a point. Neither Ed nor I had seen (Y/n) use any alchemy since she started acting differently.
"I can take 'em!" (Y/n) said, still on the ground.
"Don't make us fight you, we'll easily take you down. It's three on one!" Edward shouted, getting into a fighting stance.
"Before you do anything hasty, I'd like to say something to her," the stranger said.
Ed and I looked at (Y/n), who, after a few seconds, nodded.
The stranger sighed, putting her right hand over their mask in a face-palm manner.
"There's a few things you've been doing wrong. First of all, you're being way too outgoing and open. You're supposed to keep your feelings mostly to yourself. Secondly, you're not doing any alchemy. You've got to at least shift your automail into a weapon, like this," they clapped their hands together and touched it to their left arm. A blade similar to Ed's showed itself.
Ed and I looked between the stranger and (Y/n), confused. Why did this stranger have an automail left arm? And why could they transmute without a circle? And why were they giving (Y/n) advice on how to act?
"And one last thing. When Alphonse confessed his love to you, you gave him the wrong answer. You should have told him that you'd felt the same way for a long time now, and that you didn't care if he had a body or not. The only reason I'm talking to you in a demanding or advising tone is because I know you need me as a potential sacrifice victim. So you're not going to kill me. Isn't that right," the cloaked figure's voice started sounding more natural, less forced, and more familiar. Their hand moved to their face, pulling off the mask to reveal (h/c) hair and (e/c) eyes. "Homunculus?"
Brother and I stared dumbfounded at the newly revealed girl. It was (Y/n). But she was over on the ground at the same time. Why were there two of them!?
The (Y/n) on the ground sighed. She spoke in a voice that didn't sound like the girl I knew and loved, "Figured all that out by yourself, did ya?"
The (Y/n) on the ground slowly changed itself to reveal Envy. The homunculus stood up and walked towards the real (Y/n). He bend down slightly to be at eye level with her.
"You certainly were the easiest way to get close to the FullMetal pipsqueak and his hollow brother. They didn't suspect a thing."
"You didn't act like me. I'm certain they noticed and didn't think anything of it. Now leave, before I use my alchemy to kill you a few times," (Y/n) said darkly.
Envy laughed, "I thought you didn't like to use violence."
"You used my image to hurt someone I love. This is one of the rare cases when I will protect the ones I love, no matter what's necessary."
Envy scoffed, standing back to his usual height. He started walking away from all of us, leaving.
"See ya later, sacrifices."
We all looked after him, Ed and I shocked, while (Y/n) held a satisfied expression on her face. She turned back towards us.
"Well, that was certainly an eventful few months. I had to track you guys down after they captured me and put Envy in my place. And then I had to train, and get a disguise, and be stealthy, and think of a strategy. I'm honestly really tired," she sighed.
"Envy was traveling with us that entire time?" Ed asked, still stunned.
"Yep. But now I'm back."
"U-um, I-I'm sorry we didn't figure it out," I stuttered.
(Y/n) gave me an understanding look, smiling gently.
"It's okay Alphonse. If I were you, I'd probably have not figured it out either. I mean, if you suddenly stopped being all shy and quiet, I'd probably just think something was bothering you. I'd never have guessed that you'd been replaced or anything crazy sounding like that."
"Wait, didn't you correct Envy earlier about how he had responded in your place to Al's love confession?" Ed asked.
"Brother, shush!" I squealed.
(Y/n) looked down shyly at the ground, blush appearing on her face.
"I may have been spying on Al to make sure he didn't get hurt. And I, uh, might have in fact said that he should have made me say that I've felt the same way about him for a long time now."
I stared surprised at her. She really did feel the same way. My hopes hadn't been for nothing.
"Y-you love me back?"
(Y/n) nodded shyly, still looking at the ground.
I slowly stepped forward and shyly reached for her hand. I carefully took it and brought it to my face, placing where my mouth would be on it. This was as close to kissing her hand as I was going to get.
(Y/n) giggled a little, stepping forward more and carefully pulling my face down towards hers. She planted a small kiss on my chin, and I could tell my helmet was tinted pink.
Pulling away, she sighed. "It's good to be back."
I kept her hand in mine, interlocking our fingers. "It's good to have you back."
Brother groaned, and we both looked confused at him.
"You get replaced by a homunculus for a few months, and you think it gives you an excuse to get all lovey-dovey on me. Now I feel like a third wheel!"
I chuckled, "Imagine how we feel when you and Winry are together!"
The End.

(A/N- You guys thought the cloaked figure was Envy, didn't you? Or maybe you figured it out before hand. I don't know, I was trying to be all plot-twisty, but I'm not sure how surprising it was. Oh well, I tried!)