She doesn't have a choice

"I told you I'm not spanking your sister," protested Sara.

"We'll see," said Sam smugly.

"I'm not fucking doing it." Sara crossed her arms as if to emphasis the point. There was a knock on the door.

"Wanna bet?" Sam asked. Before the question could be answered, Tammy entered the room.

Tammy was messing about on her phone in her room when she was overcome by an urge to go to her sister's room. She had been trying to avoid seeing Sam since Tammy had been slapped by her. Tammy didn't know why but she stood up, tossed her phone on the bed and made her way to Sam's room. However with every step she took a now familiar dread came over her. Tammy began to question her sanity. 'What the fuck is going on?' she thought as she knocked on her sister's door. A second later her hand was on the handle and Tammy felt like she was entering the lion's den.

"Hey sis," Tammy tried to sound as jovial as possible despite her feelings and despite what had happened earlier in the day.

"Hiya." Sam had no need to fake her cheerfulness. "What's up?"

Tammy just wanted to get out of there and wanted to keep as far from her sister as possible, without it looking too obvious. Tammy spotted a charger by Sam's bed. It was next to where Sara sat but far enough from Sam to make her feel safe. Or at least safer. "Can I borrow a charger please?"

"Sure. No bother."

Normally this would have tipped off Tammy. Sam would never usually lend her something this easily but in Tammy's heightened state of anxiety she completely overlooked this. "Er, thanks." Tammy walked to where the charger was plugged in, keeping a weary eye on her sister as she went. 'This might be relatively painless,' Tammy thought. Unfortunately...

When Tammy entered the room, Sara could feel a strange desire build up inside her. It was a desire to inflict pain on Tammy. She had never felt like this before. Sure she had inflicted pain on people before but always with a reason, even if that reason was for her own enjoyment. However this time there was no reason, no cause for her wanting to torment Tammy. Yet as Tammy stood there that desire only got stronger. As Tammy approached where Sara sat, Sara knew not only would she act but she would also feel good doing so. When Tammy was close enough, Sara sprang into action. First she grabbed Tammy's arm and flung her towards the bed. Tammy landed face down with the top half of her body on the bed and her thighs touching the side of the bed. Before Tammy could react, Sara leapt on top of her back so her legs were either side of Tammy's, effectively pinning Tammy. Sara's body was positioned so her ass was resting on Tammy's upper back and she was facing Tammy's feet. Tammy tried to struggle when

SLAP

The first blow landed on Tammy's rump. Tammy froze. She was too surprised to react.

SLAP

Tammy began to struggle with renewed vigour but to no avail. Sam sauntered over to where her friend spanked her helpless sister, drinking in the sight and drunk on the power. She sat crossed-legged on the bed. "Just not your day is it sis?" Sam taunted.

SLAP

Sara was alternating hands

SLAP

And cheeks.

SLAP

Tammy looked up at Sam not understanding what was going on. She wanted to scream the house down, she wanted to get free but most of all she wanted to slap that smirk off Sam's face. Yet for some reason Tammy felt compelled to take her punishment and suffer in silence like she had earlier. Even as the slaps reigned down on her reddening rear, Tammy knew she would not utter a word.

Sara continued to reign slaps down on Tammy's ass. She felt like a passenger in her own body. Sara knew what she was doing but couldn't help herself. Sara somehow felt each slap had to carrya certain **** and felt like she had to do so many blows but the exact detail was beyond her comprehension. One thing she did know for certain was it felt good. In fact it felt better than good, she was starting to get turned on by the whole thing. It seemed like with every slap Sara delivered, a wave of pleasure vibrated from her hand, through her body to her whole being. Yet to some small part of her this felt wrong.

Sara was brought back to reality when she heard Tammy meekly begging. It first Sara didn't recognise the voice, then it started to dawn on her. "P-Please," it said. "PP-lleeeaase." Almost against her will, Sara delivered one final hard slap to each of Tammy's cheeks before rolling off her. Tammy remained in position.

Tammy looked up to see Sam dangling the charger in front of her face. "Still need this?" asked Sam in mocking tones. Tammy could only nod her head up and down the bed covers in response. She didn't need it however Tammy wanted it as she saw it as her only chance of escape. Sam oscillated it in front of Tammy's face as Tammy's eyes followed its path. "Then fetch," Sam said as she launched it towards the door.

Tammy needed no second invitation. She was up in a flash and over to where the charger had landed. With one hand she picked up the charger, with the other she opened the door. Only when she was outside Sam's bedroom did Tammy realise she had been holding her breath. With her tail between her legs, Tammy retreated to the relative safety of her room.

Back in Sam's room, Sara was panting hard. "Don't fucking make me do that again or I'll rip your tits off!" threatened Sara

"Yeah, whatever," said Sam nonplussed. "How do you feel?"

"Fuck off."

"No, seriously, how do you feel?" Sam was sincere this time. Sara took a few deep breaths and stared at her friend. "Good?" Sam asked. Sara nodded. "Little turned on?"

This time Sara responded verbally. "A bit."

"Fuck I'm turned on a lot. Earlier, when I spanked and slapped my sister I felt real good, like proper turned on good. Now I'm like fuck into **** or any shit like that but fuck me the power was something else." Sam looked at her friend for some kind of understanding. Eventually Sara relented.

"Yeah. I know what you mean. Even though I didn't want to get you mum in a headlock or spank your sister I'm not going to lie, I can feel myself getting a little damp down below."

"I know right. When you go I'm going to whip out my little purple friend to scratch my itch."

"So what was with the error message?" Sara asked, trying to keep a straight head.

"I dunno," shrugged Sam, "Maybe you can't do the same thing twice."

Sara wasn't convinced. "It didn't let you do it but it let me? Try it again."

With a shrug, Sam returned to her laptop and entered the same information. The error message came up: A Similar Request has been Granted Within the Past 72 Hours. Please Change One or More Fields. "Hmmm," said Sara, "Let me try something." Sam moved from her seat in front of her laptop to let Sara in. "What did you do for me to give your mum a headlock?"

Sam retrieved the image from her phone. "This," she said holding her phone to Sara so she could read the details.

Sara entered the same information into the fields except she changed her name to Sam's. The error message appeared when she hit activate. Sara changed the location from my bedroom to victim's bedroom and clicked activate. Still the error message appeared. Sara then change the follow up action from laugh it off to suffer in silence. This time when she clicked activate, Sam rose. "Back in a sec," Sam said as she walked out her room.

Two minutes later Sam stormed back into her room, full of rage. "Don't fucking make me do that again!"

"Calm the fuck down or Tammy gets her ****."

Sam froze in her tracks. "You wouldn't dare."

"We both know I would but I'm not gonna. How do you feel, more turned on? Less turned on?"

Tammy cooled a bit. "Don't get my wrong, it felt nice getting my mum in a headlock. I could feel a thrill but still, fuck you for doing it."

"Yeah, well fuck you too," said Sara with out too much care. "I think I've worked something out."

"Yeah," said Sam, trying to sound nonchalant but failing.

"Yeah. You can't have more than two things matching or it comes up with that message thingy."

"Yeah. So?"

"So you could have everybody in the world spank your sister but you would have to change where she was spanked and how she reacted. With your mum the victim was the same as well as the action but the follow up action, location and bully were different. You get it?"

"Kinda."

"Basically you can't do the same thing over and over again."

"Fairs," was the in-depth reply that Sam gave. "But we can do." Sam leant over Sara and clicked the drop down menu for the 'Action' field. "All these things to her."

I wasn't a question but Sara still replied with a "Uh-hu." Sara watched as Sam scrolled through the options. "What?" Sam had stopped scrolling. 'Hair - Cut' was the highlighted option. It was above 'Hair - Pull'. "What?" Sara asked again.

"That wasn't there before."

"What?" Now it was Sara's turn to be confused, turning her head to look at Sam.

"That wasn't there," said Sam more to herself than Sara.

"Defo?"

Sam nodded. "I think the more you use it, the more options you get."

Neither girl said anything as they let that statement sink in.