Back from the dead over here! I love this ship and it doesn't get anywhere near as much attention as it deserves. So basically this involves a personal Modern AU headcanon of mine that Eren's first relationship is with Annie who's rather fond of a certain adopted sister of his... If you don't like EreAnnie I'm sorry because it's a vital plot point here.
This fic was loosely based off the song What He Don't Know by Anarbor (very loosely indeed)
Enjoy!
What He Don't Know
"That's it Eren, I can't take it anymore!" Mikasa raised her voice. It had driven her mad. "I'm going to talk to her and get this whole mess sorted. I'm going to find out exactly why she did this to you. Stay here, drink your water and I'll be back later." She turned away from the sofa where she had been scolding Eren and stormed towards the door.
"Mikasa you don't have to-" Eren began as Mikasa grabbed her bag and keys and marched on.
"You haven't left the house since she broke up with you, Eren! I'm going to sort this mess so that you can stop drinking, clean yourself up, call Levi and tell him that you're going to be able to make it to work tomorrow. While you're at it, you can call Armin who's been worried sick about you and you can apologise for not being in touch." Mikasa rarely ranted like this. Of course she'd scolded him before, but his behaviour usually ended after that. She'd been trying to get him out of the house all week but he'd been a complete mess. She'd been Eren's first girlfriend, so he wasn't used to the feeling of a breakup. Mikasa had tried to warn him that Annie was trouble but he didn't believe her. He was excited by the idea that he was with someone that could beat him in a fight and as Mikasa wasn't really his type, that only really left him with Annie. She'd admired his enthusiasm for living and fighting for what he believed to be right. They met at the gym and they became sparring partners immediately.
Mikasa continued to her car and set off as quickly as possible, almost accidentally reversing into the car of Erwin from across the hallway. She cursed the car for not doing what she wanted before continuing on her way. Mikasa couldn't help but wonder why Annie had chosen to end their relationship. As stoic as she was, Annie had always seemed to be at the very least content with Eren. Even if it was never going to last forever, Mikasa had envisioned it lasting longer than the few months that it did. She couldn't allow herself to sympathise. Mikasa was doing this for her brother who'd spent a week in hell.
By the time that Mikasa had arrived at Annie's apartment, she noticed that Reiner's truck was gone, meaning that Annie was probably home alone since Reiner scarcely left home without Bertholdt. That was most probably for the best since things could get potentially violent with the two of them. Mikasa loosened her white-knuckled grip on the steering wheel and exhaled deeply. She needed to do this for Eren. She swung the door open and stepped out in order to reach the apartment.
When Mikasa reached the door to Annie's apartment, she knocked four times for good measure. She heard the shuffling of feet behind the door. Mikasa knew when Annie was peeking through the hole in her door when she heard the deliberately loud sigh.
"What do you want, Ackerman?" Annie asked from behind the door, the irritation in her voice obvious.
"We need to talk."
"Actually, I don't think that it's needed at all."
"Open the door, Annie."
"Why?"
"You should know how Eren reacted, you've received enough drunken answer machine messages. I just want to talk it out. There doesn't have to be any more interaction than this." Mikasa heard the locks sliding open behind the door. Annie opened the door, backing away as it opened. A very small part of Mikasa's subconscious was hoping to see that Annie was in a similar condition to Eren. Part of her had hoped to see regret, pain. Hell, just a few bags under her eyes. Something that Mikasa could have used to try and get them back together for Eren's sake. Instead, she saw Annie looking well-rested, clean and groomed. Had the breakup had any effect on her at all? Mikasa couldn't tell if there was.
"Make yourself at home, you've always been good at it." Annie grumbled, leaving the door open and walking to the main living space of the apartment that she shared with Reiner, Bertholdt and Marcel. It was a suitably large apartment since there were four of them. Mikasa glanced up to see Annie's form land on the armchair with an audible thud. She supposed that was her cue to also take a seat. Mikasa sat on the side of the sofa that was furthest from Annie. "Well, since you went to the trouble of hunting me down in the middle of the day I'm assuming you got impatient with him." Mikasa hated that attitude of hers. The attitude as though she had Mikasa all worked out just by a quick glance, smugly assuming her superiority through those ice blue eyes.
"He's suffering and it's your fault."
"So what are you going to do about it? Threaten me? Attack me? Demand I apologise?"
"I want to know why." That answered seemed to catch Annie off guard. She was on the edge of her seat, prepared to leap up if Mikasa attacked her. "I want to know what was a good enough reason to break him like that." Mikasa persisted after being greeted with silence. Annie sighed and stood up. She turned away from Mikasa and faced the large window facing an alley behind her apartment building.
"Well this is unusual for you. You're usually far less reasonable." Annie observed, refusing to turn to look at Mikasa. Mikasa stood and approached Annie from behind. "I suppose I have to let you know now. Well, simply put, my attentions were diverted from Eren."
"There's someone else." Mikasa realised aloud. However, before she could spend too long wondering who it was, she was shown.
Annie span on her heel and pushed Mikasa backwards into the nearest wall, knocking the breath out of Mikasa. Annie's arm pressed against Mikasa's chest, just above her breasts. Mikasa simply stared at her in silence, watching Annie's gaze burn through her eyes as if she saw straight into her thoughts. Annie then removed her arm only to move her hands to Mikasa's hair. She pulled Mikasa's hair so that the taller woman had to move her face down.
Their lips met. Mikasa wanted to say that it was like her other experiences with kissing, where time would pass slowly and she'd overthink the kiss and the other person's motivations. Mikasa used to worry whether her partner was kissing her for bragging rights or whether they actually wanted her or just her body but this was different. This was honest and open and Mikasa pulled a mental double-take. At no point during the kiss did Mikasa think beyond instinct. It was different. It was better. The kiss couldn't have lasted more than three seconds but within those three seconds Mikasa felt everything and nothing all at once.
Annie pulled back, loosening her hands from Mikasa's hair. She stared up, analysing Mikasa's reaction. She searched for some flicker of a smile or a grimace, some sign as to whether she should run or not. Mikasa simply stared in return. Mikasa was thinking, but Annie couldn't tell anything other than that. It was an agonising minute or so before Mikasa finally reacted. She leant down and kissed Annie again. Their kiss was rougher when Mikasa led it.
Mikasa stopped suddenly.
"So I'm the reason for Eren-" Annie interrupted her before she could blame herself for Eren's sinking into poor habits.
"It's not like you chose this. Well, just then you did, but not last week. Don't blame yourself for his reactions, that would just generally be poor decision making." Mikasa nodded before shoving Annie onto the armchair she was sat on at the beginning of their conversation, straddling Annie's lap and her hands resting on either side of Annie's head.
"Is this unfair?" Mikasa asked, staring into Annie's eyes deeply. Annie assumed that she was referring to Eren's feelings. She rolled her eyes.
"He doesn't need to know, does he? What he doesn't know can't hurt him."
Mikasa stayed for 3 hours, she then went to the gym where Eren turned up eventually. He showed up clean-shaven with burgers from Mikasa's favourite burger place, knowing that if she'd been upset from her confrontation with Annie she'd have gone to the gym. However, Mikasa was not there to work off anger from her meeting with Annie. She was there to try and create an excuse for the sweat that had begun to stain the armpits of her top and to perhaps sweat Annie's scent out of her clothing, even if it may never leave after they'd been in such close proximity for such a long time. When Mikasa saw Eren, the two hugged and Mikasa reassured him that his relationship hadn't ended because of something that he'd done and that he wouldn't have to worry anymore. He thanked her and the two siblings left the gym with Eren blissfully unaware of what his sister had done. Mikasa once again reflected on Annie's words, What he doesn't know can't hurt him.