Prompt fill for an anon on Tumblr who said- 'For your MizuSei Drabble story you said we can ask for nsfw requests! So what about Mizuki and Sei making out and getting really into and rutting on each other.'

I'd just like to say HNNNGGGG yes anon yes! rutting/grinding I just love and for these two I was more than happy to write it! I hope you like it :3

He hadn't intended it to end like this, not that he was complaining, quite the opposite in fact. They'd just been lying in bed talking, Sei on his front, propping himself up on Mizuki's broad chest. Mizuki had said something cute, though what it was had flown from his mind long ago, and Sei had giggled. That sweet, almost girlish giggle that made dark skies brighter and Mizuki's brain turn to adoring mush, smiling stupidly and leaning in for a quick kiss. Sei tasted of mint toothpaste and coffee, a bizarre mixture that somehow worked, Mizuki licking the slight dampness off his lips as he moved away, assuming they'd go back to talking. His breath caught in his throat as Sei didn't pull away, so close to Mizuki he could see each dark eyelash as they fluttered, eyes flitting from his lips to his eyes and back again. There was a second of just silence, neither boy moving, just exchanging air and watching each other, waiting for one of them to do something. Sei broke the stillness, rubbing his nose against Mizuki's gently, breath fluttering over his parted lips as the ravenette took the initiative and pressed their lips together. It was, as far as Mizuki could remember anyway, the first kiss Sei had ever initiated, too shy to try and perfectly content to let Mizuki take the lead as the more experienced of them. Clearly uncertain or nervous as to how to continue, Sei planted small, sweet pecks on Mizuki's warm lips, bartender happy to accept them and not trying to move into any new territory. Sei had practically flopped onto him by now, resting on his chest and smiling softly between each chaste kiss, Mizuki's hands on his back a warm reassurance. Growing in confidence, Sei parted his lips, leaning in uncertainly, Mizuki could sense he was nervous and met him halfway, damp lips overlapping softly. They kissed like that, setting a slow, almost lazy pace for a while, one of Sei's slim hands moving to cup the tattooists cheek, thumb rubbing circles into the tanned flesh of his chest with the other. Mizuki was reluctant to do anything that would upset or scare the smaller boy away, but he tasted to good against his mouth, feel of a smile pressed against his lips too cute to resist. So he cautiously, tentatively, poked his tongue out, drawing a line across Sei's plump bottom lip and shortly dipping it into the warm cavern beyond. A surprised breath left the ravenette, who tensed up for a moment, before parting his lips further, letting Mizuki's tongue brush his teeth. He could taste the bartender more strongly now, a mixture of cigarette smoke, breath mints and something he couldn't detect but was unmistakably Mizuki. It was a heady, addictive combination that made him bring his own tongue out to cautiously bat at the tanned mans, surprised as they brushed and his breath caught in his throat. It felt good, really good, not slimy, like having a mouthful of worms, as films had always made him think. Mizuki's fingers were firmer on his back now, one sliding up to his neck, thumb rubbing the soft skin of his throat, tilting his head so they could kiss easier.
Mizuki was on cloud nine, he'd never imagined Sei would be okay with so much so soon, especially after months of not straying beyond cuddles and light kisses. He almost wished he'd tried more sooner, but soon wiped that thought from his mind, he would never force Sei into anything, sexual or otherwise. His hands were firm on Sei's slim hips, bare skin exposed as his loose sweatpants, lent from Mizuki, slipped down his small frame. His fingers kneaded the soft skin, trying to pull him closer despite the lack of distance between them, he smelt amazing, apple from his hair and coffee from the copious amounts he consumed throughout the day. He tasted sweet on his lips, and Mizuki knew this was a scent he'd never tire of, sliding his tongue further into Sei's mouth to intertwine and taste more of that heady fragrance. Sei had been pretty quiet during it all, soft noises of contentment leaving his throat inadvertently as he made out with his boyfriend for the first time. So when Mizuki sucked Sei's tongue into his mouth and the ravenette moaned against his lips in a way that was so accidentally hot, the tattooist nearly fainted and Sei turned bright red. Mizuki needed time to recover from that, pulling away to plant soft, open mouthed kisses along the perfect expanse of Sei's neck. Treading these foreign waters carefully, he sucked a patch of skin into his mouth, nibbling at it gently before soothing it with a series of soft licks that made the ravenette gasp quietly. Positive reaction a green light for Mizuki, he bit with more force, focusing right over one of the blue veins that ran under the translucent skin, lavishing it with attention. Sei's breath hitched, making a needy, keening noise in the back of his throat, the next thing Mizuki knew he'd flipped the smaller boy over and was straddling him. There was a pause as they both caught their breath, just staring at each others warm, flustered faces as Mizuki wondered if he'd gone too far. He was soon proven wrong as hands knotted into his hair and he was tugged back down, insistent lips hot and wet on his as tongues brushed and their bodies pressed together. Sei made another needy noise, fingers pressing into tanned skin as he tried to get more, although more of what, he wasn't sure. It was so hot, the feeling of Mizuki's dominating frame on top of him, almost pinning him in place, the hands on his body were insistent and desiring, wanting him and him alone. His eyes, which had been shut this entire time, fluttered open in shock as Mizuki adjusted his position, inadvertently rubbing their lower bodies together, alerting Sei to his erection for the first time. A breathy moan left his kiss-swollen lips as unfamiliar pleasure coursed through his body, Mizuki groaning softly against his lips in a way that made Sei light headed.
The bartender reluctantly pulled back, resting his head in Sei's neck as he caught his breath and arranged his thoughts, arousal dimming his sense. This was too much, he knew that, too much too fast, he should stop before he couldn't resist anymore.
"Mizu?" The voice that floated down was clouded with lust, but still soft and concerned, hand caressing his back muscles gently. "Are you okay?"
"I'm fine, Princess." He replied, planting an innocent kiss on Sei's neck before moving so he could see his boyfriend once more. His breath caught in his throat as their eyes met, Sei's pupils dilated, lips pink and swollen and hair in disarray against the pillow. The first word that came from his lips was a short, breathy "fuck." He internally cursed his lack of suaveness, but God Sei looked so fucking hot.
Sei had flushed pink at Mizuki's announcement, feeling an unasked question hovering in the air between them and looking at the tattooist expectantly.
"Do you-" Mizuki began, pausing to think about how to word it, 'do you want to carry on?' sounded too forwards, and carry on to what exactly?
"Do I what?" Sei breathed, the atmosphere was still heavy and he was waiting for Mizuki's question with bated breath, knowing this would change things between them irrevocably.
"Do you want to stop?" Ah, now that sounded okay. That gave Sei total power over the situation, he could either say yes and they would stop, or he could say no and they would continue to whatever end he was comfortable with.
Sei bit his lip, unable to meet Mizuki's eyes as he thought about it. He liked the way Mizuki felt atop him, a heavy weight, he wanted more, he needed more, but he didn't know what he needed more of. He was embarrassed admitting it even to himself, but he wanted Mizuki to touch him, he wanted it to feel good again, he wanted to make Mizuki feel good. He knew he wasn't ready for.. that, but he knew there were other things, and as he kept reminding himself, if it's Mizuki, it's okay. He still refused to look at the bartender as he shook his head no. He didn't want to stop, he didn't know what was going to happen, but he felt safe with the tanned man and knew he'd be fine as long as it was Mizuki he was with.
Mizuki's breath hitched, noticing the vivid blush on Sei's cheeks with a smile and reaching up to stroke his warm cheek, "You sure?"
"Mm-hm." Sei nodded, leaning into Mizuki's touch and meeting his eyes, face twisted into an embarrassed pout that faded as the bartender kissed him softly. Or at least, it started out softly, but both of them soon gave in to their desire and the atmosphere became heavier, Mizuki's arms sliding under Sei to pull him closer, fingers digging into pale flesh. Sei's fingers were insistent on Mizuki's sides, and he knew if the bartender was wearing more clothes this would be the point where he'd be trying to pull them off. As it was, Mizuki's fingers slipped under the waistband on Sei's sweatpants, encouraging the dark boy to lift his hips so he could wriggle out of them, leaving him in black, tight fitting boxers. The line of his erection clear through the fabric, any embarrassment was gone as Mizuki continued kissing him hungrily, making needy noises in the back of his throat. Mizuki's sweatpants went next, tangling round one ankle and making Sei laugh until Mizuki nipped his bottom lip, pulling him into another kiss and it turned into a moan instead.
Sei was small and fragile under him, skinny arms wrapped around his waist and pale fingers roaming the muscled flesh of his back, feeling it tense and relax as Mizuki shifted slightly. Desperate for some sort of friction on the matching bulge in Mizuki's boxers, the bartender ground their hips together again, groaning as sweet sparks of pleasure shot through his groin. Sei's breathy gasp and erratic, sloppy kisses only encouraging him to continue, rubbing his hips down onto Sei's and feeling their hardnesses rubbing together through the thin material of their underwear. Sei's head was swimming, he'd never felt anything so good before, arching upwards to meet Mizuki mid-movement, their clothed erections rubbing and producing such delicious friction. Everything made Sei feel even more flustered and aroused, Mizuki's pants and moans, the feel of firm skin against his own, the hands on his hips holding him in place, fingers digging in almost painfully. Mizuki groaned hotly against Sei's lips as he held him down, grinding into him unashamedly, feeling a damp patch growing on his boxers as he became more and more worked up with every rub of their crotches.
Sei could hardly breath, the air was heated and thick and his brain swam with pleasure and Mizuki's hands on him and Mizuki's smell and Mizuki's taste in his mouth and Mizuki Mizuki Mizuki..
Already the pleasure was building, a strange pooling feeling in the pit of his stomach as he whined and pressed back against Mizuki, friction against his dick so perfect and needed. Pink lips on pale skin came up to kiss and nibble at Mizuki's adams apple, sucking flesh that had a tang of sweat into his mouth and releasing it. Hips moving more erratically as the bartender moaned and panted, fingers pressing into pale hips hard, probably leaving red marks that might even bruise, but Sei wasn't complaining. The heat continued to build in Sei's stomach until all he could do was whine brokenly and pant and groan Mizuki's name as his orgasm rushed to meet him.
"Miz-u! Ngh- ah!" He moaned, pulling the bartender closer to him, shoving their sweat-coated bodies together and burying his face in the junction between his neck and shoulder, biting down hard with a moan so broken it sounded almost tearful as he came suddenly, jerking upwards into Mizuki's hips.
Mizuki wasn't sure whether it was the amazing friction, or just the noises Sei was making that brought his own orgasm crashing over him, but with only a couple more thrusts he came too with a cry of Sei's name. Collapsing onto Sei's exhausted, panting body he was barely aware of the grossness of his boxers, instead trying to catch his breath and relaxing his hold on the smaller boy.
"Fuck, Sei." He laughed breathily, pressing a kiss to the ravenettes damp forehead and smiling as a pair of shaking arms wrapped around him. Sei made a happy sort of sigh, meeting Mizuki's eyes with a content expression and a mild blush, leaning upwards for a short but sweet kiss. They lay there for a while, limbs entangled and sticky underwear forgotten about as they just enjoyed the warmth of each others bodies in their shared afterglow. But of course they couldn't stay like that forever.
"I feel really gross.." Sei remarked, suddenly becoming aware of the drying fluid in his boxers and squirming uncomfortably.
"Mm, me too." Mizuki replied. "Shower?"
Sei looked too exhausted to even move, but nodded slowly. "Carry me?"
The bartender chuckled softly, brushing Sei's hair out of his face before having a thought. "Let me wash your hair and we've got a deal."
Sei looked surprised for a second, but then grinned and nodded, allowing Mizuki to climb off him, immediately missing his warmth which was replaced a second later as he scooped him off the bed easily. Carrying him bridal style to the bathroom, pausing to turn the light on and surprised when a pair of lips met his before he could.
"I love you." Sei whispered, dark room not as frightening as it would normally seem as he lay safe and comfortable in Mizuki's arms.
"I love you too, Princess."

Okay, so usually for rutting/frotting fics I prefer Sei on top, but because I've written this as being their first time doing anything like this I thought it would be more IC to have Mizuki be on top leading the way sorta thing.
also, who wouldn't want Mizuki on top of them? :P (haha don't look at me I'm DMMd loving trash)