Prompt from ObeliskX:

What if someone decides to play a joke on Eren and Mikasa: add laxative to their juice glass, just as there is sparring coming next day. As he looks at them waiting, nothing happens... Actually some components were messed and created completely different potion. When next morning Mikasa and Eren awake, to their shock and horror they find themselves in new bodies.

Title: The Alchemist (Gender Flip)

Characters: Eren, Mikasa, Jean, Krista, Ymir, Armin, etc.

HUMOUR & FRIENDSHIP

Rated : K+

Levi stood in front of the new recruits of the Scouting Legion with Hanji by his side. He let out an audible sigh clearly displeased with the conclusion he was about to voice. He had argued with Hanji for hours on end prior to this meeting, trying to express the importance of his opinion, but it was always the same with Hanji. No matter how much you fought, she always won the argument.

Now he stood in front of the Scouting Legion, given the job to grace everyone with a day off. Whoop-de-doo. Typical Hanji, she fought with all she had to make her point that a day off would spread relaxation throughout legion and refresh their mindsets. Then after Levi had finally agreed with her, she made him make the announcement, making him look like the soft one. Like these little brats deserved a break, they were hardly working now, let their minds fill with death, that's how you learn how to deal with it.

Levi stepped up on a box, any other veteran in the legion that needed a box to become intimidating and commanding would elicit laughs, but not many dared to mock Levi.

Levi commenced with a snarl, but sucked it up.

"Well you brats, as of recent discovery, we have found that you all seem overwhelmed with the high levels of trainingwe've been giving," Levi's own words caused him to scoff. "So you get today as a break. You have no scheduled training for today and can do anything within the city limits."

And with that Levi stepped off his box and walked back to his cabin in disgust, leaving behind the cheers of the Scouting Legion.

"Guys can you believe that we actually get a day off," Eren screamed to Mikasa and Armin.

"Seriously, it's the last thing I expected from Lance Corporal Levi," exclaimed Armin.

"What do you guys want to do? I don't know what to do with all this freedom," Eren joked.

"Well we could go to the Trost Market. It's only on this weekend."

Eren didn't miss how Mikasa's expression brightened at Armin's statement. When they were kids they always visited the market in their hometown and Mikasa always loved it.

"Yeah I could go for the market," Eren agreed.

"Alright let's head over then."

As the trio approached the market, there were tents upon tents set up full of various items and foods. Everything one could ask for could be found and bought at the Trost Market. However there was one booth that caught Eren's attention. As Mikasa and Armin pointed out various booths and planned out their routine for the day, Eren snuck off to explore his new discovery.

Eren stalked over to the purple tent titled Alchemist. It didn't take much to catch Eren's attention, but lots of bubbles, colours and smoke definitely did it. Eren approached the tent browsing the multitude of potions laid out on the table. The alchemist was a short man, with a long grayish white beard and gray hair that parted in the middle. He wore a long coat that almost resembled a robe and carried a cane that looked a lot like a stick. He stood in the back of the tent working on one of the potions.

Eren yelled out to him, "Excuse me sir!"

The man just kept mixing ingredients and tossing things into the concoction he was formulating in his apparatus.

"Sir!"

With that the man spun around startled and looking very unsettled by the shouting.

"Huh, what are you doing here kid? No one ever comes to my booth."

"Well your potions attracted my attention and I just want to know what they do."

The man stood there for a few seconds still surprised that a customer had approached his booth. That was until he noticed the cadet outfit and the wings of freedom on the boy's coat.

"Ah you are in the Scouting Legion, eh?"

Eren looked down at his outfit, always forgetting that he was wearing it since it had become his daily attire. He released a rise smile before replying with a yes.

"I was in the Scouting Legion once upon a time. Back when it originated. I've been retired for many years now due to an injury to my leg."

"Oh really, wow that's amazing! I mean not the injury part, but yeah you know…"

"You know what? I know exactly what you need kid."

The man squatted down under the table and reached into a box pulling out a wooden lock box. He reached into his pocket and pulled out a key inserting it into the box and unlocking it. He reached into the box and pulled out a pinkish red potion in a flask.

"This concoction contains a special mixture of herbs and spices combined to form a potion that will double your strength."

"Seriously? This is exactly what I need."

Eren knew this was his chance. This potion was his chance to prove himself in his human form. This was his chance to defeat Mikasa in combat; this was his chance to prove to Mikasa he wasn't a child. That he deserved his freedom and didn't need to be taken care of. Without a single doubt crossing his mind, Eren had made his decision to purchase the potion.

"I'll take it. How much?"

"You know, for a fellow soldier like you, I'm willing to make an exception. This one's on the house."

"Thank you Sir!" And with that Eren saluted the man as a sign of respect and went off to find his two friends.

Eren walked through the market in search of his friends, but kept getting distracted by the different booths. It seemed hopeless that he would ever reunite with Armin and Mikasa. Until someone came up from behind and latched on to his ear, something very reminiscent of what his mother would do when he misbehaved.

Eren turned around cursing and yelling at the bestower of his pain. It was Mikasa, of course it was Mikasa, and Armin standing next to her laughing and shaking his head.

"Why do you always have to treat me like a child!?" Eren yelled at Mikasa.

"Why do you have to run off like a child?" Mikasa replied staring daggers into him.

Eren didn't back off, staring right back at her, resembling a stand-off before a boxing match. Armin had to interfere before someone threw a punch turning it into a real boxing match.

"Eren what's that in your hands?" Armin asked.

That seemed to do it, snapping Eren's attention to Armin and causing his eyes to brighten up again.

"It's a potion I got from the alchemist guy over there! He gave it to me for free. It's supposed to make me stronger and more powerful."

This elicited a face palm from both Mikasa and Armin.

"Eren, those local alchemists aren't trustworthy. The ingredients aren't listed on the bottle, so you have no idea what is in the potion. You have no idea what they could've put in the mixture or what process was used to create it."

That was enough to send Mikasa into a panic. Her protectiveness pulled through and she reached to grab the bottle out of Eren's hand, instantly causing Eren to spew a vast variety of complaints.

"Mikasa, what the hell! What are you doing?" Eren yelled holding the bottle away from Mikasa as she attempted to pry it out of his hands.

"Eren you heard Armin, it's dangerous! Give me the bottle!"

"Don't tell me what to do Mikasa, you're not my mom!" And with that Eren took the bottle, pulled the cap off and began to chug the drink.

Before he could drain the bottle however, Mikasa pinched Eren's ear again causing him to drop the bottle into her hand.

"You're so stubborn sometimes Eren, it's unbelievable," Armin mocked.

Mikasa however didn't say anything, she just glared at Eren. A few moments of silence passed before Mikasa took the bottle and tilted it killing the rest of the liquid. This caused Armin's mouth to drop and he just stared at Mikasa, all the while Eren's ears and face grew red as his infuriation reached another level.

"What is your problem Mikasa! You can't stand the fact of me being stronger than you! That's what it is, isn't it? You can't live one day where I'm stronger than you! You're so selfish!" Eren ranted before storming off back towards the camp.

"Eren wait! You don't understand!" Mikasa yelled after him.

"Armin I just didn't want him to suffer alone, it had nothing to do with strength," Mikasa tried to explain to Armin.

"I know Mikasa, I know. You know how he is," Armin replied. "We should probably head back to camp as well, it's getting dark."

"Okay."

Eren awoke to the usual sounds of the Scouting Legion horns resounding throughout the camp. Every morning at six, training never rests is what they told us. He continued with his usual routine, getting out of bed, brushing his teeth and combing his hair. He did all this while half asleep, it was the regular routine now and Eren could practically do this in his sleep. He was pretty close to that right now honestly. His eyes were closed as he brushed away and rinsed and spit. He was finishing up when he splashed his face with water and that's when he saw it.

Mikasa's routine wasn't much different. She spent a little more time combing her hair than Eren did, but other than that, everything was similar. If Eren could do this in his sleep, Mikasa could do it without breathing. Even with her strength and dedication, Mikasa was the same as the other recruits, never wanting to wake up in the morning. So she did her entire routine with her eyes closed, trying to steal a few more minutes of sweet sleep. She wasn't the first one to notice, the first one to notice was Sasha when Mikasa had asked her to toss something from across the room.

. . .

It wasn't long until Eren came busting through Armin's door.

"Where's the fire?" Armin joked.

Then he looked up. Eren could've sworn he saw Armin's jaw drop to the floor and he didn't blame him. There were no words from either of them. They both stood there staring at each other, Eren looking desperately for something, anything and Armin just in pure shock and confusion. It looked like Armin was about to say something when the door flew open once again. Mikasa skidded through the door practically bowling over Eren, her mouth moving a hundred miles a minute with unanswered questions. Unlike the silent encounter Eren and Armin shared, Mikasa wouldn't shut her mouth and was pleading for some sort of solution.

Her mouth ran and ran and Armin didn't answer one of her questions. He just looked back and forth between Eren and Mikasa as if he was watching a tennis match. Mikasa was starting to get frustrated with Armin's silence until she finally turned her head and saw Eren standing there staring right back at her. His or shall I say her long eyelashes and flowing brown hair framing her face. Her lips looked plumper and the baby fat on her cheeks had diminished. The most amusing part, if there was an amusing part, was the way her uniform fit her newly sculpted body. Her shirt was way too large at the ends, hanging down to almost her knees with her newly acquired melons not helping with the shape of the shirt stretching it to suffocate her upper torso. Her pants were not much different, her added junk causing her pants to strangle her legs. That was when Mikasa finally went silent.

Eren on the other hand, had been silent the entire time. At the start it was due to his desperation towards Armin, but now it was because he couldn't believe what was in front of his eyes. Mikasa was no longer the girl he had grown up with. His hair was about half the length it once was with his bangs cascading across his forehead, making him look like a member of a boy band. His cheek bones were more prominent and his chin was sculpted like a model. His lips were thinner and light stubble was growing on his face. His uniform didn't fit much differently except for the fact that his shirt almost ripped at the location of his newly acquired broad shoulders. His shirt was getting pulled upwards slightly exposing his abs, one thing that didn't change and the loss of fat in the rear caused his pants to sag with his boots just a tad tight.

They both stared at each other, looking like they had just seen a ghost. Not a single word exchanged, you could almost touch the tension in the room. Then there was a laugh, a single laugh, an escaped laugh from across the room. It was as if a child had accidently let out a laugh in a funeral full of silence and mourning. Except this child didn't stop, his laughing only grew. Armin couldn't control himself, he couldn't stop, it was just too hilarious.

"If only you guys could see what I'm seeing right now," Armin broke out between gasps of air.

"You think this is some kind of joke-"

"Armin are you seriously laughing right now-"

Eren and Mikasa were furious and their inaudible yells couldn't be deciphered. It didn't help Armin's laughing fit as it just made the situation more juvenile and hilarious. He probably could've laughed all day if he hadn't seen the faces Eren and Mikasa made as they marched towards him with their fists up.

"WOAH! WOAH! Okay calm down, I was only joking." Armin pleaded cowering behind his arms.

"This isn't a joke Armin!" Mikasa screamed.

"Okay, okay, I'm sorry, just calm down."

"It's a little hard to calm down when we look like this!" Eren countered.

"Okay first of all; Eren I told you so."

"Is that really helpful right now!?"

"No, you know what, he's right! If you would've listened to us in the first place, we wouldn't be in this situation right now!" Mikasa directed at Eren.

"Oh really now?! Don't you even start with me Miss 'I need to protect Eren. I must be stronger than Eren. I must baby Eren.' You didn't have to drink it in the first place!" Eren countered back.

Eren and Mikasa stared into each other's souls. If looks could kill, Eren would be buried six feet under right now and Mikasa would be there with him, still staring at him. Armin actually feared for Eren's life, there wasn't many moments were Mikasa seriously lost it on Eren. Yeah she got frustrated with him all the time, but to get to the point of wanting to murder her adopted brother, well that was a new level.

Armin was sure it was going to happen, if it weren't for Jean walking in. Everything in Armin's mind prayed for Jean to keep his mouth shut, for his own safety. But of course, Jean was Jean, and Jean wasn't going to exist on this planet anymore in about one minute.

"I always knew you were a girl Eren."

That was when all hell broke loose.

A few cuts and bruises later, Eren, Mikasa, Jean and Armin reported to combat training. Everyone stood in the usual line awaiting instructions from one of the Captains in the legion. Except the difference today from different days was everyone staring at Eren and Mikasa, including the Captains. It was already frustrating enough to deal with this alone, but having everyone stare at you just made things much worse. Mikasa had enough self-control to contain his anger, but Eren on the other hand, she did not.

"What in Sina's name are you guys staring at, huh? You want a piece of this!" Eren yelled enticing the others to fight.

This evoked Connie to let out a cat call like whistle, frustrating Eren even more.

"Eren calm down man, I mean girl… Sorry," Armin tried to relax Eren, but having trouble containing his own laughter.

After a few minutes of staring and whispering, the Captain finally snapped out of his trance to try and maintain order.

"Alright, listen up! Today we are going to continue practicing combat training! Today everyone must match up with a member of the opposite sex. In the Scouting Legion we celebrate gender equality, no one gets mercy! Partner up, let's go!"

The second the Captain released the recruits, everyone scattered to find a partner. Armin paired up with Annie, Sasha paired up with Connie, Jean attempted to pair up with Mikasa like usual, but quickly realized that was no longer a possibility. Eren frantically searched for someone to pair up with, first trying with Armin who apologetically chose Annie, then trying Connie but just receiving laughter as an answer, and then there was Jean, yeah not happening. Then the last person Eren wanted came to her, Mikasa.

"Eren just because we switched genders still means we can partner up."

"I don't want to partner with you."

Before Eren could counter, the Captain interrupted, "Well that's too bad Eren because there are no more boys to partner up with, so stop fooling around and spar with Ackerman!"

Eren mumbled a few curses to himself before taking the ready position.

"Let's just get this over with," Eren sighed.

Mikasa charged at Eren, he wasn't sure if it was the frustration from the situation or just adrenaline, but he grabbed Eren with new swift speed, tossing her to the ground. He felt immediate regret because he never wanted to hurt Eren, no matter what gender they were.

"Eren I'm sorry, I didn't mean to."

"Don't pity me Mikasa, I can take it."

With that, Eren surprised Mikasa by tackling him to the ground. She pinned Mikasa down, straddling his chest with her legs and holding down his shoulders.

"Eren do you mind removing your boobs out of my face," Mikasa joked.

"I can barely keep them out of my own face Mikasa, how do you girls deal with these things? They keep punching me in the face," Eren said seriously.

"Like you have the right to complain. Have you seen my wardrobe, all my gym clothes are short shorts and sports bras, how am I supposed to wear that now?"

That elicited a chuckle from Eren and soon enough both parties were rolling around in laughter of their predicament. The silliness and insanity of everything finally got to the both of them and they couldn't control themselves. Everyone in the exercise stopped momentarily to stare on at the two who had lost complete control of their emotions.

Eren and Mikasa both knew how stupid they looked, but they couldn't help it. The whole situation was ridiculous. However from that day on, everything seemed to go up.

Mikasa gained new strength with his transformation, his broad shoulders and chest and now natural muscle mass helped him and the Scouting Legion. He began to quickly move up in the ranks. The higher ups were impressed with how much Mikasa had improved on his already amazing talent. After Levi had gotten over the annoyance of Mikasa's new body, he was even surprised with how much Mikasa had improved since the transformation.

The girls in the Scouting Legion even started to hit on Mikasa a little. The biggest surprise was when Annie came to Mikasa one night. Usually the two biggest rivals in the Legion, who seemed to despise each other, were now getting along. A little too well if you asked Eren. It wasn't just Annie though, it seemed male Mikasa was a hit with the ladies, as he had lines of girls lusting for him.

This didn't bode well with Eren. She already was frustrated about Mikasa moving up in the ranks and started to get worried about all the dangerous missions and drills they were putting him through. Eren was beginning to get super protective of Mikasa and what had become of him.

That was when Eren finally came to a realization. She started to realize why Mikasa used to be so protective of him. She started to get it. She started to understand the reasoning that Mikasa babied him back then. Why she followed him everywhere and why she tried to prevent him from going on dangerous missions. Eren felt real bad about how she had treated Mikasa in the past.

Eren found Mikasa later that day to apologize for the past. That was the very moment that Armin came to them with an antidote. He had gone to Hanji the very first day that Eren and Mikasa had discovered their new bodies. Weirdly enough she didn't seem surprised at all by it, if anything she looked annoyed and said she had exactly what they needed, it would just take a couple of days. Now a couple days later, she had found Armin and given him a flask of her own containing the cure to everything.

Armin handed them the potion and gave them some space, exiting the room. At first Mikasa grabbed the bottle fully prepared to drink it and solve all these troubles, but Eren stopped him. She debated with Mikasa if it was beneficial to switch back and apologized for everything she had done in the past. No matter how much they wanted to go back to their original sexes, Mikasa was naturally stronger as a male and the Scouting Legion could use him. Eren on the other hand was less stubborn as a female and she didn't have to worry as much about Mikasa bothering her and could focus on training. They debated for what seemed like an hour until Armin came back into the room.

"What're you guys waiting for?"

THE END

A/N: Alright I'm really sorry to the person who asked for the prompt, I know I took a long time to write it and I'm not going to make excuses, I apologize. Okay so I apologize if the story wasn't exactly matching to your request, but I had to change some things to match my style and for the background context to be better for my planned plot. This is my first time writing a gender flip premise because I don't usually read them or particularly enjoy them to be honest, but ObeliskX had a different spin and twist on their prompt that intrigued me and I hope you liked it either way! Also I understand that Titan Eren and Trost are both intact at the same time, but just imagine that they are for this story. Let me know what everyone thought.

THE FIRST DAY

As Eren walked away, the alchemist stalked off in the opposite direction. He walked around to the back of his tent, stopping a few feet behind the market. He dropped his cane which in reality was just a stick and removed his coat. He reached up to pull off his beard and discard his wig. He brushed his hands together in maniacal relief that his plan had pulled through.

"I always knew that Eren was too stubborn. That'll teach the brats to have a day off," Levi snarled.