Imagine being Derek's mate and omega but your stiles sister and you decide to scare the pack by testing out an experiment 

Fandom: Teen Wolf

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You and Derek had met and been dating after a few months before stiles and Scott had met him and every time someone saw you there was rules set in place but the only rule you had for Derek was that he couldn't hurt stiles in any sense of the term or you would leave him alone for the duration of the healing process or till you felt necessary to go back to him and that was once when he hurt stiles on accident

Everyone that had joined or left between the two packs and now into one everyone had been told of the rules and punishments of touching you and such which everyone followed since they didn't like Derek being all mad and such when he wasn't with you even if you were gone for 5 minutes

So, every pack meeting had to start with you being there and if you weren't they waited for the sake of their lives more than anything so even if you were tired and wrapped around a blanket that smelt like Derek then so be it

So, when you both had a few weeks alone you walked up to Derek who was doing his hanging workout in the house while you walked in and sat on the stairs

"Derek, I want to do an experiment would you want to participate in it?" you asked as you played with your hands

"And what's your experiment?" he asked not stopping but looked like he was going to slow down since he sensed that it wasn't going to continue any time soon due to you wanting his attention

"I want to fake breakup to see what happens with the pack" you replied after a bit as he got down and turned to you and looked at you over the banister railing

"a fake breakup?" he questioned walking to you and stopped when his feet hit the bottom step of the stairs

"Yes, telling the pack we broke up and see who would take their first shot at me if we do properly breakup which would be never due to us being mates" you replied looking up at him in slight fear that he was going to reject the idea

"Fine but you must remember that you have to wear something of mine so that you can have my scent, so you don't constantly smell of them" he replied softly as he leaned down and rested a hand on your cheek which you leaned into

"And I'll leave my blankets here" you replied with a small smirk "oh and don't hold back on the angry sourwolf Derek it won't work if you do" you replied with a small chuckle making him nod in agreement

So, in the next pack meeting you and Derek were already in the loft and you started arguing over random stuff that both pissed you off but when you both heard them going to the door to open it you growled slightly and backed away from him

"You know what that's it were through I can't handle you when you're like this" you spoke out annoyed as you turned to walk out and saw the whole pack there which made you shake your head annoyed and walked off while Derek stood there upset but angry slamming his hand on the table

"Woah what just happened?" Jackson asked as stiles went and followed you who was already halfway down the road

"isn't it obvious Einstein she just broke up with Derek" Lydia spoke as she hit Jackson before they all walked into the room to comfort him but stopped when he growled at them to leave, and they did and had the pack meeting at Scott's house

Just as you arrived at your house with stiles since he didn't let you drive home you got a text from each male pack member making you chuckle a bit when you got to your room, so you scolded them that you just went through a breakup and told Derek amused

After a week of not seeing Derek in a couple sense and acting like you broke up every boy was wanting you and showering you with gifts, but Derek was making their lives hell with the way training making them not get a wink of sleep without feeling pain when they moved

After a few days the boys noticed you still wore Derek's clothes but they thought it was because you still cared while he didn't to their eyes but they all wanted to go to you and ask Derek to stop with the intense training but was too scared to do so until Aiden came over

"your going to have to suck it up and tell Derek to stop" he spoke out calmly as he looked at you with concern in his eyes as you looked up at him annoyed

"I am not going to that loft for as long as I live" you shot back before slamming the locker shut and went to your lessons

"well, that worked mister I've got this" Isaac replied as he watched you go before wincing in slight pain as his patted his shoulder and Aiden did the same but didn't show it

A week had passed and nothing was done about it despite Isaac whining at you like a puppy to get Derek to ease up on the training but you let him down nicely compared to the rest of the team especially when they made Stiles talk to you but since he knew he didn't care but that still didn't mean that they didn't still try to get you but Scott, stiles and the girls figured out what was going on after seeing you and Derek on a home date one night but didn't say anything

So one day when school ended you went straight to the house knowing the boys all had lacrosse practice you had flung your bag on the couch and walked over to the table in the middle of the living room passing Derek

"Ok experiment over I can't handle it" you spoke out as you watched Derek workout "like how they cannot figure it out I mean the girls have and Scott and stiles but not the rest" you added pacing the room

"who doesn't figure it out Aiden or Jackson?" he asked chuckling as he got down and wiped the sweat off with a towel before putting it to the side and held you close making you take in his scent which was soothing you a bit since you hadn't seen him a few days due to pack meetings being a Stiles house where you were mostly staying in

"All of them" you muttered into his chest as you wrapped your arms around him and curled into him

"Don't worry it will all be over soon" he whispered "they finish practice, and they will come to the loft, and we will tell them simple as" he added pressing a soft kiss to your forehead calming you more

After a few hours the boys came back to the loft all talking to themselves on who gets you since Derek didn't have you to call his but when they walked in, they saw you and Derek training since you both walked over after a while, and he pinned you against the wall but not with force and they didn't see it that way, so they growled, and Derek let you down lightly

"what's up with you? were training while you were at practice Jesus" you sighed shaking your head as you fixed your clothes a bit while Derek watched them wearily while protecting you

"Ok then sorry but who are you going to pick?" Isaac asked fiddling with his hands looking down before backing up at you cutely

"of course, it's going to be me who would reject this sexy body" Theo replied causing you to gag slightly making him look at you offended and everyone else laughed and Derek to smirk amused

"What about Isaac he is cute" Lydia smirked since she knew making you walk up to him, and Derek growled protectively which made Isaac back away from you slightly

"Spoil sport can't I just look that's not harming anyone" you pouted at Derek as you walked over to him and grabbed his chin slightly before forcefully moving my hand from it then moved to sit on the chair by the table

"And besides Derek she's not even yours anymore so why do you care" Jackson sneered watching him with a smirk which earned Derek to growl at them again and they jumped in fear bar Lydia and Allison

"She still is" Lydia pointed out as she leaned against the wall checking her nails

"Since when?" Aiden asked shocked at the newfound information as he looked between Lydia and Derek

"She never broke up with him it was all an experiment which you all failed at clearly" she sighed as they watched you move to sit on the table next to Derek and hug his arm slightly since you didn't like the distance

"It was an experiment if you will...I wanted to see what you guys would do if I left Derek and how long it would take you to jump to get me and it only took 10 minutes of you guys finding out to see if I wanted someone else" you explained as Derek leaned against the table with his arms crossed so you moved to lean against his side

"a mate is a mate for life for an omega to fully date someone else the alpha in this case is me has to dump and or reject the omega to fully date someone else and since she broke up with me that didn't work with the mate bond" Derek explained as he looked down at you for a bit before back to them with a small glare

"But if I had to choose to date someone else when this sourwolf leaves me would be Isaac" you spoke out after a bit with a small smile as you jumped off the table and kissed Isaacs cheek softly before going back to Derek who growled at you slightly to scold you which didn't work as you pecked his shoulder softly not fearing him

As you made your decision every started arguing about your choice of who you would have instead of him, but you just curled into Derek acting all cute and innocent while he stayed stoned faced letting you do what you wanted to keep you happy