Side with Ava

You make a quick decision to help the obviously stronger sister. You run up to them and swiftly slide your foot under Mia's, putting her off balance and letting Ava take the upper hand. Ava quickly pins Mia to the ground, face first. Ava keeps one of Mia's legs in place with one hand, and both of her arms with the other. Mia tries to squirm out of her position but is unable to. She stops struggling and sighs in defeat.

She says "OK, FINE, you got me. So what now?"

Ava is breathing heavily, but still manages to reply by saying "Now? NOW?? Now, you'll get punished for messing in other people's business. But, since I'm a bit tired, I'll have my partner start things off. Go ahead dude, fuck her ass!"

Your eyes widen at her remark, but you feel like you shouldn't look a gift horse in the mouth at this point.

You get down on your knees, behind Mia's round ass and take your dick in your hand. It's already half hard, from watching the naked bodies of the girls wrestle one another, so it only takes a couple of strokes to make it fully erect.

Before you place it in Mia's tight asshole, Ava speaks up "Hold up, let me lube her up for ya..."

She lets go of Mia's leg and spits a big wad of saliva in her hand. Surprisingly, Mia doesn't seem to make an escape attempt. Could it be that she's enjoying this? Either way, Ava starts smearing her spit covered hand all over her sister's asshole. She slips two fingers in Mia's anus, making a tiny yelp escape her lips. Ava starts fingering her sister's ass, lubricating the inside and outside of it. When it feels lubed up enough, Ava removes her hand from Mia's wet ass and starts rubbing your cock. Her hand is warm and slimy, while her smooth skin rubs against your hard cock. You could probably cum from just Ava's handjob, but there are more important things to get to...

When Ava let's go of your cock, you take it with your own hand and press it against Mia's asshole. Thrusting forward, your cock easily slips halfway in Mia's ass, making her moan in response. The tight walls of her anus feel amazing. You slowly start moving your cock back and forth until you feel comfortable enough to speed things up. With a powerful thrust, you send your dick all the way down her anus, making Mia spurt out a long moan of pleasure. Your 6-inch dick isn't anything special but seems to be doing the job just fine with Mia.

After a while of fucking the white-haired girl's ass, you feel that you are close to cumming. You smash your hips against hers a few final times, before pressing hard against her body, as you unload your cumshot straight down her ass. After you're done cumming, you close your eyes for a bit, trying to collect yourself. When you open them back up, you notice that something is wrong... Ava isn't holding her sister down anymore! Although Mia doesn't seem to be escaping, you can't help but wonder where Ava went.

Suddenly, you feel a warm breath on your neck, and a quiet voice saying "My turn..."

Before you get to react, you feel something hot and wet press against your butt. When you finally realize what's going on, it's already too late... Ava has gone behind you and is now attempting to penetrate you, which she does easily. Her dripping wet cock slides in your ass, making you flinch.

Ava says, through a hearty moan, "Oooohhhh, that feels good. Watching you fuck my slut of a sister got me so excited, I just had to fuck SOMETHING. Since you were so busy with this bitch, I thought you wouldn't mind a little attention too. Now let's get back to fuckin'!"

Ava thrust her giant member all the way down your ass, making you moan with a mix of pleasure and pain. The **** that Ava put in her thrust, sends your own cock back into Mia's ass, making her moan too. You are now sandwiched between both of the sisters, being fucked by Ava from the back and being practically **** to fuck Mia. Ava starts thrusting her entire lengthy shaft in and out of your tight ass, making your body move forward and put some extra energy into your own thrusts against Mia. Since you already just came, your cock feels numb for the first few minutes of the fuck session, but the sperm you shot up in her makes for a perfect lubricant to get things going again. Soon enough, you find a rhythm with Ava and Mia, making your thrusts more efficient. Mia pumps deep in your ass, and at the same time, you thrust into Mia, as she moves her own hips back to get your dick down her own ass faster. She really seems to be enjoying this.

As Ava's thrusts get harder and faster, so do yours, making all three of you moan and breathe heavily. Mia sounds the most excited in this situation, almost like she can feel both your and Ava's dick fucking her ass at the same time. You, however, feel amazing. Your prostate is being fucked hard, making your cock feel even better as it slides in and out Mia's, now stretched, ass. And Ava is just having a grand old time ravaging your anus. Soon enough, you feel Ava's dick get hotter and stiffer, meaning she's close to orgasm. Your own cock starts throbbing more and more. With the joined moaning picking up in volume and frequency, everybody orgasms at the same time. Ava grabs hold of you tightly and shoots giant loads of sticky white cum straight in your rectum. You can feel it filling you up, but you're too concentrated on your own orgasm. You spray a noticeably larger amount of jizz down Mia's ass, mixing your previous load, although it's still not as big as Ava's. Mia's eyes roll back in her head as her ass and prostate get pumped, making her ejaculate all over the floor, almost shooting a steady stream of semen all over it. After your orgasm has already subsided, the girls still indulge in theirs.

When everybody has finally calmed down, Ava is first to pull her schlong out of your dripping ass, and taking a seat on the couch. You also, slowly, rip yourself from Mia's tight ass. It's more difficult than you expected, as Mia's anus grips on your dick, almost as it not wanting to let go. You manage to free yourself and take a seat next to Ava. You both stare at the ruined sister on the floor, and she seems to slump down and fall to sleep, cum running out of her ass and drool escaping her open mouth.

Ava looks over to you and says "Thanks for having my back there, kid. It felt really good to finally GIVE it to her. Hope you don't mind me having my way with you."

"Not at all!" you reply.

She continues "Great! Well, I'm probably just gonna head back to my room. I'm sure when this slut wakes up, she can find her way to the room on her own. You probably got business to take care of yourself, so I won't keep you waiting. Bye for now!"

She stands up and happily walks away. You wave and she waves back, before disappearing through the door she came out of. You get up as well, take a look at the sleeping girl on the floor, and get back to your own room, still a bit sore from Ava's cock.

You got the "Double-edged sword" ending with Ava and Mia.