Danny moaned into the shoulder of his current partner as he buried his cock up to his balls in his asshole. The man’s asshole was the tightest asshole he’d fucked.

Fuck you feel good, he murmured into the skin of his partner’s shoulders.

Fuck me Leo, the man beneath him whined.

Shut the fuck up Cas, the man positioned along the wall behind Danny growled.

Sin, fucking stick your cock in my ass and fuck me or I’m gonna pull out of Cas and stick my cock up your ass while Cas sticks his cock up mine, Danny snapped. Or would you rather have your brother’s cock up your ass?

The only reason Danny wanted Sin’s cock up his ass was because it was massive. Fully erect, it measured no less than 11 inches in length and at least four fingers in girth. And Danny was a sucker for a massive cock because only a massive cock could hit his prostate just right and make him cum like nothing else. A breathy laugh came from a chair in the corner.

Sin has never fucked a guy before, it said. Perhaps he should start with something he knows.

Sin growled at her but said nothing. He merely took Danny by the hips and pulled him back onto his massive cock. Danny moaned at the slow pace of penetration and tried to impale himself on Sin’s massive cock. But Sin’s grip on his hips prevented him from doing so. Cas squirmed beneath him. At last, Sin’s balls brushed his own. Danny groaned in pleasure. He looked over his shoulder and crooked a finger at Sin. Sin leaned forward and Danny captured his lips in a passionate kiss. Sin reached around and cupped Danny’s balls. Danny gasped into Sin’s mouth and Sin’s tongue took advantage of the opening and plundered the depths of Danny’s mouth. Cas whined and squirmed beneath him. Danny motioned to the corner of the room. The person moved into the light. The girl was no older than 18 but beautiful and well endowed. She stood naked before Danny and his partners, her stepbrothers.

What do you want from us, Thea? Danny asked pulling away from Sin’s mouth.

I want you to fuck each other to the brink of cumming but I want you all to cum in me. She was bold. Danny would give her that.

Why do you want that? He asked pulling Sin into another kiss.

Because I’m an experiment that needs to be tested. She replied.

Oh? Danny answered barely breaking away from his kiss with Sin.

I was given multiple uteruses and ovaries. She replied. I’m old enough to see if they work properly or not.

We’ve all been genetically modified, Thea. Danny replied. We all have to be tested.

And I’m not saying the three of you can’t continue after I get all of your cum where I want it. You can wait and go another round.

Little sister, you don’t seem to understand, Cas growled. We only get one ejaculation a night and it took quite a bit to get Astinos to agree to this.

What if I told you I knew a way for you to get multiple ejaculations in a single night.

Then I say you’d better tell us so we can get on with fucking each other so we can fill you with our cum, Danny grit.

There’s a switch sitting near your balls, she told them. It’s been sitting in neutral since you were genetically modified. Flip it up and you can get hard multiple times and you can cum multiple times.

Show us, Danny demanded.

Thea went to Cas first, since he was closest, and ran her fingers along his scrotum. Cas moaned and pulled her into a passionate kiss. She pulled away when her fingers found what they were looking for.

Fuck me Cas, she whispered into his lips.

Cas surged from Danny’s grip and immediately buried his cock in her pussy. She managed to turn so she was beneath both him and Sin. While Cas fucked her, she ran her fingers over their scrotums until she found the switch.

Fuck him, Astinos, she ordered.

Sin was more than happy to comply. Danny felt him begin to move. Slowly at first but he picked up speed as his pleasure mounted. Astinos pulled him into another kiss.

My cock and my cum are the only ones allowed in your asshole. I don’t care who you fuck. Your ass and your womb are mine.

If my ass and my womb are yours, then your ass and your womb are mine, Danny murmured against his lips.

Sin gave a savage growl and began to fuck him harder. Danny could feel Sin’s massive cock begin to swell. He was close to cumming. Danny knew as soon as Sin started cumming he would be hard pressed to keep from cumming. Just then Cas gave a savage cry and came hard inside Thea. He pulled out and Thea, noticing he was close, made her way to him and began to fuck herself with his cock. Moments later, Sin came with a loud roar. Danny following him not long after. Danny pulled out of Thea and watched in satisfaction as cum slid down her legs. Sin went to pull out but couldn’t. Danny didn’t tell him about the knot that formed because he’d made the promise that Danny was the only one he’d fuck. What they were experiencing was known as the mating knot. It only appeared in genetically modified assassins and alchemists who had essentially said wedding vows to each other.

Astinos you’re next, Thea hummed.

You’ll only get me the way Danny just used you, he growled finally pulling out of Danny’s ass. Danny is the only one I fuck now.

Danny’s flaccid cock twitched at Sin’s statement.

You only get to have my cock once and only for its cum to test your modifications. Otherwise my cock and my ass belong to Danny now.

Then who will fuck my ass? Cas demanded.

I will.

All eyes turned back to Thea, who was now palming something that looked very much like a flaccid cock complete with balls. As she palmed her cock, it grew hard.

Have you always had that? Cas asked nodding to the rapidly hardening cock in her hand.

It’s another modification, she said with a shrug. Do you want this?

Cas swallowed hard before nodding. Thea pounced on him and drove her erect cock into his ass. Sin wrapped his arms around Danny and pulled him close.

Are you ready to take my asshole virginity? He whispered in the shell of Danny’s ear.

Danny turned to him and kissed him.

I’ve wanted to take your asshole virginity since the day I first saw you, he whispered against Sin’s lips. Do you know how badly I wanted your cock in my ass? I could tell the day you walked into headquarters that your cock was not only the biggest I’d ever laid eyes on but that you knew how to use it.

You could tell how big my cock was?

Of course I could tell. The way you walked was the biggest indicator. Danny palmed his cock. With a cock like this, is it any wonder I call you Sin?

Sin palmed his cock.

You want this? You want me? Danny teased.

I’ve wanted you since the moment I saw you flaunting your latest conquest around headquarters, Sin nipped at his jaw. I can’t tell you how many pussies I fucked trying to get you out of my head.

You sound like you’re more than ready for me to fuck your brains out, Danny rasped.

Sin gave a jerky nod that had Danny spinning him around and bending him over the bed faster than Sin had thought possible. Lust swam in Danny’s eyes as he began to sink his cock into Sin’s virgin asshole. From somewhere behind them, Thea and Cas both gave guttural moans before collapsing in a sweaty, cum filled heap. Danny shook his head at them. They were spent. But he and Sin were still relatively fresh. Thea must have looked over and seen him fucking Sin because he could hear her moving towards them.

Don’t forget your promise, she told them her voice gruff and definitely lusty.

Only Danny can agree to sharing my cum with you, little sister, Sin said around a moan. My body, my cock, and therefore my cum belong to him so only he can agree to share any of it with you.

Fuck! We had an agreement! Thea nearly shouted.

That was before Sin knotted me, Danny growled possessively.

Cas stared at Sin in shock.

You knotted him?!? He demanded.

What like you didn’t knot Thea and she didn’t knot you? Sin countered lightly.

Both Cas and Thea looked away in embarrassment.

Sin, honor the agreement now before I get too possessive of you, Danny growled into Sin’s ear.

He pulled out of Sin’s ass, causing him to whine.

Spill quickly and come back to me so I can finish what I started and knot you, Danny murmured in Greek.

Sin stood quickly on shaky legs and barreled into his stepsister. Thea barely had time to react before he was buried up to his balls in her cum covered pussy. Danny watched in possessive amusement as Sin fucked his stepsister hard and fast. Danny knew he’d been close to cumming but he didn’t know how much self control Sin had.

Asmodeus, Sin whined plaintively in Greek. I need to cum.

Then cum, Danny ordered.

I can’t! Sin whined. I need...

What do you need? Danny asked soothingly. Do you need my cock? Sin nodded helplessly. Do you need my knot? Sin nodded vigorously. Then take what you need.

Sin shook his head.

I can’t.

You can’t take what’s freely given, is that it?

I can’t take from you. I want you to give it to me freely.

And that’s exactly what Danny did. Danny gave him the fucking of a lifetime. Sin held on for two of Danny’s powerful thrusts before he came hard into his stepsister’s cum covered cunt. He pulled out before his knot could form and Danny rewarded him by increasing his pace.

Fuck me Asmodeus, Sin moaned in Greek. Ah! Yes! Fuck! Hit it again! Fuck me. Fuck me. Fuck! Knot! Knot....now! I....need....knot....FUCK!

Sin went limp against Danny as he shot rope after rope after rope of scalding hot cum into his womb. Danny’s knot formed before the first jet of cum coated Sin’s womb. That alone was unusual but what made it more unusual was its size. Most knots, according to all the data the Alchemists had, were the size of a small baseball. His, on the other hand, was the size of a softball. When his knot subsided he pulled out. It was then that he noticed Sin’s cock was still erect. He pulled out of Thea before he could knot her. His cock needed to knot or things could get bad. Danny sighed and moved into position in front of him. He drove Sin’s cock into his ass and came again. Sin groaned as Danny fucked himself with his cock. It wasn’t long before Sin’s knot formed and he coated Danny’s womb with ropes of scalding hot cum.

I say we call it a night, Danny said gently maneuvering Sin into bed, which was easier said than done with his knot still hard in Danny’s ass.

And the sleeping arrangements? Thea asked.

Sin’s already out, Danny answered. Cas in front of me and Thea in front of him.

And what about our cocks? Thea asked.

Your cock doesn’t have anything to go to but mine and Cas’s do. If you don’t want Cas’s cock in your cunt, get over it because it’s either that or your ass. As for my cock, it’ll be buried in Cas’s ass all night. I won’t knot him but I may fuck him a bit.

Fuck away, Danny, Thea told me. Hell you can knot him for all I care. I just wanted your cum.

And why is that exactly?

Why else? I want a baby in each of my uteruses. One from each of you. I don’t care about anything else. I just wanted your semen. No, more like I needed it.

You knotted Cas and he knotted you. I can smell it. Danny told her.

So? Thea demanded.

So you can’t walk away from him, Sin replied groggily. And he cannot walk away from you. The two of you are bound together more completely than marriage. And you can’t undo it.

Fucking watch me, Thea growled.

Danny was about to reply when he doubled over in pain. He hadn’t felt pain like this since Iri had taken Jamie’s pain after he broke several bones. That was years ago. This pain could only mean one thing; Iri was taking Jamie’s pain. Danny didn’t know why he could feel when Iri was taking Jamie or Mac or Niall’s pain more than his other siblings but he did. Sure, when Mac and Iri were in Scotland it didn’t matter. But now that they were in the states and in close proximity to him, he could fucking feel every time Iri took their pain. And it fucking pissed him off.

Asmodeus? Sin’s voice was soft but rough with sleep.

Go to sleep Sin, Danny told him. I have to go see my brother.

You’re not going to...... Sin trailed off tears gathering on his lashes.

Danny kissed him, hard.

I would never do anything like that, he growled.

Promise? His voice was small and fragile.

Of course. How about this, when I get back I’m gonna knot you until you can’t walk tomorrow. How do you like the sound of that?

He said the last part in Greek so the others wouldn’t understand it.

In reply, Sin nearly tackled him and ground his cock against Danny’s. Danny gripped his balls.

Save that for when I return, he growled playfully.

Another jolt of pain stabbed him. Danny sucked in a sharp breath.

Fucking hell Iri, he grit.

It felt like knives were running down his forearm. He had to get to Niall before things got any worse. He threw on a pair of boxers, not even caring if they were actually his, and stumbled to his brother’s room.

Jesus Danny! What the fuck? Niall snapped.

Iri’s taking Jamie’s pain and it’s not good, he panted.

His arm felt like it was on fire.

What the fuck happened? He growled.

Koschei happened, Niall deadpanned.

What the fuck Niall?!? You let Jamie deal with that sick fuck ALONE?!?

Please it’s not like I knew Koschei was going to get out! Niall snapped.

You might as well have let him out! You pushed her buttons didn’t you?

Danny narrowed his eyes at his brother. Of course trust Niall to royally fuck things up and leave Jamie to clean up the fucking mess. Danny’s no better sometimes but at least he knows not to bring out any of the entities residing inside his sister.

Danny why are you wearing boxers that are at least 2 sizes too big for you? His uncle asked.

It was then that Danny noticed the boxers he’d grabbed were in fact Sin’s. Which would explain why they were falling down.

Uh grabbed the wrong pair, he shrugged.

There’s no way you just happened to grab the one pair of boxers that’s too big for you, Niall rolled his eyes.

Danny shrugged.

Wait, his uncle said.

What? Danny asked cautiously.

His uncle stood and limped over to him.

You smell different, he murmured taking deep breaths as he circled Danny. It’s not simply the fact that you just had sex, there’s something else underneath it.

Fuck, Danny thought. He’s got to be smelling the fact that I was knotted by Sin. That or he’s smelling the fact I knotted Sin. Either way, this isn’t good.

You..... he began. You’ve been knotted. And recently too. That’s not all. You’ve knotted someone too. And not a woman.

You knotted a man?!? Niall growled.

Why do you even care who I knot or who knots me? Danny demanded.

God you’re reckless! Niall snapped.

A knock sounded on the door. Niall went and wrenched it open.

What the fuck do you want? Niall spat.

I heard yelling, the voice said.

Danny knew that voice. It was Sin. Danny went to the door and shoved Niall out of the way just as another spike of pain lanced through him and drove him to his knees gripping his arms.

Fuck! He cursed.

Asmodeus? Sin asked.

Danny turned to his brother.

Go fucking clean up your mess before our dumbass sister kills herself! He thundered before clinging to Sin, who was kneeling beside him.

He took slow, measured breaths to try and breathe through the pain coursing through his arms.

Asmodeus, what’s going on? Sin asked.

My fucking idiotic sister is taking my brother’s pain, he grit.

Suddenly, Danny gave a guttural scream and collapsed against Sin.