Disclaimer: I don't own Vocaloid

[20/3/14] Note: Ok, to get this out of the way, I wrote this quite a while ago and I'm really embarrassed about how crappy the porn I used to write is (but hey, we all have to start somewhere! Not that I'm amazing today but my writing has at least improved from this.) I edited this one last time so it isn't as cringe-worthy, but please keep in mind I was fourteen when I wrote this. I should probably rewrite it from scratch but it's a bit too much work for me right now, though I might revisit this fic in the future.

Kaito was used to being the top.

He was used to being the one who would thrust into Len's hot, tight ass over and over, revelling in the sensations and the pleasured moans he would hear every time he would move.

So when Len finally had his Append upgrade installed, he was somewhat bewildered. Though his personality was mostly the same, his body was not; and as subtle as those changes were, he couldn't help but notice them. His voice was more well developed (Kaito wouldn't admit it, but he still got goosebumps whenever Len said his name), he was noticeably taller (though still shorter than him by a few inches) and his body had definitely matured.

It turned Kaito on.

He supposed, at first, that it was normal. Len, after all, was his lover and had been for quite some time. This thought placated him for the most part of the day, until Len decided to try on his new outfit.

And damn, Kaito thought, Len looked hot. The way the fabric hugged him in the right places, its intricate detailing creating an alluring silhouette and revealing just the right amount of skin – it drove him wild.

That explained why when Len entered his bedroom to ask for some hair gel (because his had run out, no surprise) wearing nothing but a towel around his waist, his hair still wet from his shower, drops of water running down his now slightly more well defined abs, Kaito snapped.

He found himself pinning the younger boy to the wall, running his hands across his damp skin, leaving a trail of slight kisses from the corner of his mouth to his neck; his tongue darting out to catch the occasional droplet of water. Kaito smirked against Len's skin as he heard his breathing start to slow and deepen. He circled a tongue around one of Len's erect nipples, making him moan as he lingered for a few moments before moving to the other. Len started to whine as Kaito pulled away, only to have his mouth captured in a deep, passionate kiss.

Kaito was surprised (though not at all in a bad way) when Len began to respond right away, pulling him closer, his tongue gently but assuredly wrestling with the his own, when, usually, he would wait and let Kaito ravage him until he became so aroused he couldn't stand not to do anything. Kaito broke the kiss and let out a breathy groan when Len began to grind against him, hand moving to explore his chest under the fabric of his shirt.

Len, on his part, was completely stunned at how he was acting. He was fully aware of what he was doing, but he didn't try to stop himself, didn't have the desire to. Somehow, he just wanted to feel the heat of Kaito's skin under his palms, to feel him squirm as he caressed every inch of his body. He wondered, during a short moment where he wasn't completely preoccupied with the body pressed flushed against his, if this was how Kaito usually felt when he was in his place, before Kaito took off his shirt and pulled the both of them onto the bed.

They kissed - half kneeling, half sitting on the large bed, their bodies intertwined, hands wandering heatedly. Kaito let out a moan when Len stroked his erection through his pants.

"You're already so hard," Len said, a little out of breath, applying more pressure to his cock. Kaito shuddered as he started to feel his pleasure build as Len continued to touch him. He half-gasped, half-groaned and reached out to pull off the towel wrapped around Len's waist.

Through his lust-filled haze, Kaito wondered how Len's cock could have grown so much in such a short amount of time. The last time he had seen it (which wasn't really that long ago), it wasn't much bigger than his palm. Now, though, as he stroked it, Len moaning and jerking under his attentions, he noticed he could somewhat comfortably wrap hand his around it. It made him wonder, in the back of his mind, what else about Len would surprise him next.

He cried out as Len began to thrust against him, managing to stroke against cock in a way that left him unable to hold in his voice. Len pushed him down and undid the zip of his pants, Kaito's head too clouded to protest, his body feeling too good for him to even want to.

He was brought back to earth by the feel of Len's warm lips wrapped around his cock, his wet tongue caressing the tip of it. Len moved down on him, sucking harder as he did. Kaito moaned and he shuddered uncontrollably as Len ran his tongue along his length, head bobbing as he fucked his mouth with Kaito's cock.

He felt his release near, his body tensing, when Len abruptly pulled away. He whimpered as Len pinned his hands to the bed as while fought desperately in an attempt to come because he was so close. When he had begun to come down, worn out but unsatisfied, Len leaned down and kissed him hard, releasing one of Kaito's hands to play with his erect nipples.

He broke the kiss and began to move downwards, nipping and sucking at Kaito's neck, his chest, his stomach. Kaito held his breath as Len moved, teasing him by slowing his pace he moved lower, lingering and leaving small marks on his skin. He clenched his teeth as Len neared his cock, but was surprised when he only brushed past it and pulled his legs apart, running his teeth over the sensitive skin of his inner thigh.

Kaito gasped when he felt Len' tongue at his hole, licking at the furled skin, relaxing him, before slightly pushing in. Len licked him inside and out, fucking him with his tongue, making Kaito shudder at the sensation, before he pulled away and smirked, making a show of licking his fingers before positioning one in front of Kaito's hole. He pushed it in all the way before pulling out, slowly and deliberately so Kaito felt every inch. Kaito let out a heavy breath as Len pulled it out to reach somewhere behind him, only to groan as Len pushed two lubed fingers inside him, scissoring and opening him up, adding a third finger a few moments later. Kaito let out a moan as the friction of the fingers inside him began to make a dull pleasure reverberate throughout him. He spread his legs further and lifted them slightly to give Len better access, only for his hips to buck violently when Len brushed against what must have been his prostate, the sensation so intense he had to bite his tongue to keep from yelling out.

Len stopped and pulled his fingers out, a small sound of protest escaping Kaito's throat as he did. He grabbed the bottle of lube and slicked himself up, almost painfully hard after preparing Kaito, and positioned himself between his legs, hooking the other man's feet over his shoulders. He pressed the tip of his cock flush against Kaito's hole, and for a moment the room was dead silent except for their harsh breaths, then Len pushed in and Kaito screamed.

He felt Len fill him, the heat of his cock almost too much. Len caught his prostate again as he began to thrust, and every time he did, Kaito would see white with the pleasure. Len let out a choked groan when Kaito began to tighten around him, trying his best to hold back, not wanting to move too fast before he was sure Kaito was ready.

Kaito moan loudly, his voice echoing around the room. "God, Len, fuck- please fucking move."

At the sound of Kaito's wrecked voice, Len lost it. He let out a grunt and began to thrust frantically, plunging the whole of his cock deep into his hole before pulling it out almost all the way. He leaned forward and caught Kaito's lips with his, giving him a hard kiss before he shifted to a better position, supporting his weight with his arms. Kaito ran his hands through Len's hair, tugging gently, keening as Len hit his prostate over and over. The sound of slapping flesh and heated moans echoed around the room as Len pounded into Kaito's hole, and he cried out as he felt his orgasm build. He wrapped his hand around Kaito's cock and began to pump, wanting him to come before he did. The combined sensations drove Kaito wild – his arms tightened around Len and screamed his name as an all-consuming orgasm ripped through him, his nails digging into Len's back and come splattering at the crook of his neck. Len's thrusts grew erratic and he came moments after, Kaito tightening around him as he came too much to bear. He continued to thrust as aftershocks riddled both his and Kaito's bodies until his cock began to soften, and he pulled out collapsed on top of Kaito, exhausted.

When Kaito finally managed to pull himself from the drowsy, contented haze he was in enough for his brain to begin functioning, the first thing he noticed was Len's (more well developed, upgraded sexy-hot) body in his arms, his (slightly more heavily-muscled) chest gently moving up and down as he slept.

The second thing that registered in his mind was what they had done for him to get there. He winced at the burn he felt in his ass when he shifted a little.

He thought for a moment, and concluded that maybe it was all right to bottom more often. Probably.

He smiled and pulled the blankets over Len, careful not to wake him up as he manoeuvred him into a more comfortable position, deciding that cleaning up could wait until his legs didn't feel like jelly, and snuggled into the blonde's still-damp hair.

I apologise if anything still sounds painfully awkward, or if there are any glaring grammatical errors (let me know if there are), as I didn't bother re-checking after I edited this.

Sorry about any alerts that might have been sent out! :D

Thanks for reading!