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2026-05-24
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lessons in chemistry

Summary:

kai has been harboring a not-so-secret crush on his study buddy all year. what will happen when he gets an unexpected text asking if you can stay the night?

Notes:

originally posted to tumblr

Work Text:

Kai had been infatuated with you since the start of last semester. The two of you sat near one another for a large science lecture. It was a gen-ed filler class for the both of you that you were just trying to get out of the way. Kai was a first year music major and you had just switched majors from fine arts to liberal arts and suddenly found yourself in need of a few more required science credits.

He fell in love with you the first moment he saw you, sitting down a row ahead of him in the dim lecture hall, the low light illuminating your features. Twice a week for three weeks he admired you fondly from his unofficial assigned seat. His notes were often lacking- sentences missing from the slides that he forgot to copy down while lost in the thought of you instead. You were the highlight of the dull class for him. He’d never forget the way his heart almost leaped out of his chest when you finally turned around to smile at him. Your smile was warm and inviting as you asked him to be your partner for an assignment. He’d never been particularly suave, but the stumbling, stuttered “yes, of course” he replied with was enough to make him want to curl up in a ball. But you just giggled, your laugh like music, accepting it in stride.

From that day on he was your study buddy, never missing a library date. The two of you worked on assignments together, studied for exams and shared snacks late into the night.

You grew close over the course of the semester, inside jokes blossoming between the two of you. You were older, more organized than he was. You knew your way around campus and the city and you were eager to offer your advice. You laughed at his jokes and loved to hear the recordings he made of his guitar and piano playing. As friendship grew between the two of you, so did his feelings for you.

Anxiety swirled in his head as winter finals approached, unsure of whether or not you’d be in the same lab section as him in the spring. He worried that if you weren’t, he’d lose his chance to talk to you. When you told him your schedule- classes aligning perfectly with his- he almost hugged you then. Relief flooded his chest, thankful for the chance to see you twice a week for an additional four months.

His friends had caught on to the fact that he was crushing on someone; they saw the way his eyes lit up when certain notifications flashed on his screen. They had been nudging him to invite you to study at the dorm, even promised to clean it so he wouldn’t be embarrassed to bring you by. But you lived off campus in your own apartment. Why would you ever want to hang out in his shared dormitory? No, he’d just keep doing what he was doing: being your cute and reliable study buddy.

----

You knew Kai had a crush on you.

It was obvious in the way he texted you back immediately, even when you knew he’d swipe away notifications for the rest of his friends. Obvious in the way he shifted in his seat if you leaned over his shoulder to look at his notes. Obvious in the way he practically vibrated out of the chair the first time you decided to sit next to him in the lecture hall instead of a row ahead. He always brought your favorite snacks and packed your favorite drinks when you met up for study sessions. You couldn’t remember telling him what your favorites were either, he just paid attention like that.

You didn’t mind, in fact, you liked having the cute boy’s attention. Kai was tall and broad and dorky and shy, but you had gotten him to open up to you, bloom like a flower into sharing his silly and passionate self. Kai was a good friend and a bit of an ego boost as well. Here was this tall boy with sharp cheekbones who cared about your thoughts and opinions. So, so what if you caught him staring down your shirt when he was supposed to be copying your notes? It's not like you hadn't stared at his ass in his jeans more than a few times.

And truth be told, you really did need him as a study buddy.

----

The cool of winter was slipping away to spring, first flowers peaking their heads out of the damp earth. Kai was losing his mind.

His friends had figured out more about you and the extent of his devastating crush and were making bets on how he would fumble you. Beomgyu had struck a particularly sensitive nerve with the simplicity of his bet: that Kai would just never get the nerve to ask you out for more than a library study session. It was stupid and it wouldn’t normally piss him off, but he was scared that they were right. He didn’t want to miss his chance with you.

You had become really important to him over the course of the school year and he couldn’t stand the thought of you just being a class friend, someone he lost after finals ended. He already experienced that anxiety when he worried about your spring schedule, but had lucked out despite his inaction. He wasn’t sure what he’d do now that the end of the school year was approaching.

----

The soft patter of rain filled the spaces in between notes as Kai worked on his piano final composition. He knew how the piece started, and how it ended, but he struggled to find the perfect rhythm to pull it together. He had been locked in his room for hours, long fingers dancing over the keys again and again, trying out new arrangements and then scrapping them when they weren’t right.

Nothing was right. Dejected, he pushed his chair away from his keyboard, pulling off his headphones and huffing as he reached for his phone, needing a distraction. He frowned when he saw two missed calls from you and a string of worried texts.

Hey soooo…

I left my bag in my ta’s office and I they won’t answer any of my emails and I don’t have their number

and my keys were in my bag…

and now I can’t get in my apartment 😅

and all my other friends are out of town...

can I please stay with you?

Kai called you immediately. You picked up on the second ring.

“Are you okay?” He asked worriedly.

“Kai! Oh my gosh you called me back! Thank you so much, I wasn’t sure-”

“You can stay here.” He said quickly.

“You mean it?”

“Yes.” He was organizing his room as you spoke, throwing dirty clothes in the hamper and wrapping up charging cables. “Do you know which building I’m in?”

“I think so. I’m actually not too far away.”

Kai could hear the rain as you spoke, muffling your voice. “Oh gosh, do you have an umbrella?”

You laughed sarcastically. “Haha, no, but I’ll be there in ten minutes. Can you come down to let me in?”

“Yes, yes I’ll be there. Do you need me to stay on the phone?”

“No, uh, it’s actually getting kinda really wet. I’ll just meet you in the lobby.”

“Okay, stay safe. I’ll meet you in the lobby.”

You hung up and Kai immediately ran to his roommates to fill them in.

----

You were soaked head to toe when you walked into the small lobby of Kai's dorm building. He was nervously shifting his weight between his feet as he waited for you to arrive. His voice was laced with worry when he ran over to you, asking how you were doing the second you walked through the double doors. His worry was cute. You liked how much he cared.

“I’m okay, just cold.”

The elevator ride up to the dorm Kai shared with Taehyun and Beomgyu was filled with a charged silence, broken only by the patter of droplets falling from your clothes onto the floor. You hadn’t met either of his roommates yet, but you’d heard stories. You weren’t sure if you’d meet either of them tonight either, but all you really wanted to do was change out of your soaked clothes and go to bed.

Kai apologized for things being messy before opening the door, but he had no need. The small shared space was cleaner than expected for three college-aged boys. Each had their own room and then a shared kitchen and bathroom. You followed Kai to his narrow bedroom.

His standard-issue twin xl was filled with plushies, a grey bunny which was clearly the oldest and most well-loved sat in a place of honor in the very front. It made you smile, this display of softness. Beside the bed was his desk and keyboard just beyond that. The space was cozy with the low light of a singular bedside lamp.

You turned around to face the room’s owner where he stood in the doorway, suddenly awkward in his own space. “Cute room. I like your plushies.”

Red blush immediately tinged his ears. His eyes fell to the floor as he awkwardly laughed. “Haha, yeah um, I can move those.”

“You don’t have to.” The silence between you was still charged from the elevator, but you could barely focus on it with the way the cold rain had settled into your bones. “Um, is it okay if I take a shower? I’m freezing.”

“Oh! Uh, yeah- of course! I have an extra towel. Do you need clothes?” He began to rifle through his drawers. “I think mine will fit you. What do you want?” He was cute the way he looked over at you as if picturing each item in the drawers on your body.

----

Kai sat on his bed anxiously bouncing his leg as he waited for you to finish in the bathroom. He was trying his best to suppress the thought of you in the shower, water falling over your curves. He shook his head, trying and failing to shake out the thought of the river of soapy bubbles running between your breasts, trailing down over your plush tummy. But even if he shook that thought, there was still the fact that you would exit the shower and put on his clothes and then get in his bed. His head was spinning with possibilities.

His leg was bouncing fast enough for it to start to cramp by the time you walked into his room. His ears burned as he took you in. His dark pullover clung to your figure, settling at your hips. You smiled at him before turning to hang your towel on the back of his door. Oh no, he thought. He had fished an old pair of basketball shorts out of his drawer for you to sleep in since your clothes were hung precariously in the bathroom in an attempt to dry them. The fabric was stretched tight around your hips and ass, leaving little to his imagination. He stifled a groan at the sight when his hoodie rode up to show the dimples on your back as you reached up to throw the damp towel over the hook.

You looked so good in his clothes it made his head spin. He wanted to see you in his clothes all the time, wanted you to show everyone you were his. Wanted you to be his for real.

He was sure he looked like a wreck when you turned around, cocking your head to ask what he was thinking. “I um, did you- did you eat?”

“Yeah, I ate dinner before I saw my TA.” You sat down beside him on the bed. He could feel the warmth radiating off your skin from your hot shower. “Actually, um, I know it’s kind of early, but this whole thing has been really stressful and I’m just really tired.”

“Yeah, that’s okay. I’m sorry this happened to you.” He practically vibrated when you rested your head against his shoulder, not even caring if his shirt got wet.

“Not your fault.” Your voice was soft. “Thank you for letting me crash. I can’t tell you how much it means.”

“It’s no problem. I’d do anything if you asked.” Kai wasn’t sure how much he wanted you to read into that sentence.

----

The two of you talked for a bit before a big yawn prompted Kai to ask you about sleeping. He insisted that he’d sleep on the floor for you to take his bed. You argued back that you could take the floor since it was his room and just one night wouldn’t hurt you but he wouldn’t budge. You finally conceded and found yourself tucked under his covers next to his army of plushies.

The room was dark except for the dim glow of campus peeking through the blinds and the multicolor lights of his pc that lit the space with a shifting neon hue. You rolled over to peak over the edge. Kai was laying on the floor face up, hands over his chest. He was wide awake and his eyes immediately found yours. “Hey,” he whispered, “you should be sleeping.”

You couldn’t stand the fact that he was sleeping on the hard floor, shitty dorm carpet against his back and a throw blanket the only thing to keep him warm. This was his room after all. And beyond the injustice of kicking him out onto the cool floor, you didn’t want to let the opportunity to be wrapped up in his strong arms pass you by. “Can you please come up here?” You could see his eyes widen and before he had the chance to argue you used the line he couldn’t refuse. “I’m still really cold.”

He sputtered cutely, looking for words. “Are you sure?”

You kept your voice quiet as you pleaded; “Please Kai.”

He didn’t say anything as he stood up and climbed into the small bed. You moved to the far edge of the mattress, positioning yourself against the wall. You wondered how he slept comfortably here each night, his large frame filled up most of the narrow space, and you doubted that his feet weren’t hanging off the edge. With your body taking up space too, there was no way for the two of you to not touch.

Kai was shy with his actions, reverting back to the unsure boy you met at the beginning of the school year. “Um, uh- is this okay?” He asked as he gingerly settled his arm across your waist.

“Yes, perfect.” You backed up to snuggle into his broad chest. Heat radiated off of him, warming you instantly. “Mmmm, you’re so warm.”

----

Your body fit against Kai's like his matching puzzle piece. His arm slotted perfectly in the space between your tummy and chest. He felt like he was made to hold you just like this. This moment was perfect, everything he could've asked for after pining after you for months. He could breathe in the scent of your skin and hair, still slightly damp from the rain and shower. Here you were, in his clothes, in his bed, in his arms. He was on cloud nine. Everything was perfect.

Except for the fact that you kept wriggling your hips against him.

You had to be doing it on purpose. As far as he could tell you were sleeping, but the subtle movements of your ass against his front were driving him crazy. He had backed his hips up as far as he could given the narrow twin bed, but yours had followed. He prayed that you were asleep and wouldn't notice his half-hard dick pressed up against you.

He thought he was in the clear, your hips had slowed and he thought he'd make it through the night without embarrassing himself. He could do this- sleep with you in his arms then get up and jerk off in the morning before you woke up and it would be like nothing happened, like he wasn't cuddled up next to you thinking about how his hand was so, so close to your chest and your ass was so warm against him. He'd savor this moment for what it was and then make his move later. But then you spoke.

“Kai,” your whisper pierced through his thoughts like a hot knife, “are you hard for me?”

His mind blanked. Fuck, he was really in it now.

“It's okay if you are.” Your hand found his, drawing gentle circles on his palm. You continued playing with his fingers as the silence stretched, charged and electric between you. Kai didn't breathe, hanging on for what would happen next. “You know, I've seen the way you look at me.” You wiggled your hips again, slow and deliberate. “Saw the way you blushed when I came in here with your clothes on.”

It felt like Kai was on fire. His body blushed and he could feel the blood rushing to his cock. He felt guilty, caught in the act. “I know you have a crush on me Kai.”

He wanted to protest, began to speak a strangled “I-” but you cut him off.

“I have a little crush on you too.”

Your words knocked the air out of Kai's lungs. His head spun. You were in his bed, in his clothes, holding his hand, pressing your ass against his dick on purpose and you liked him back. He felt like he was short circuiting.

He could hear the smile in your voice when you whispered again. “You can touch me if you want.”

----

The silence stretched between you longer than you expected. Part of you worried that you had misread everything, that you had crossed a line. But after what felt like eons Kai's hand finally moved.

His fingers twitched in your grasp, fingers splaying out and holding onto your tummy over the sweatshirt. You were silent as he began to slowly move down, curiously slipping under the thick hem. You drew in a breath quickly when his fingers brushed against your skin. His fingers were slightly calloused from playing guitar, the rough pads of his fingers leaving goosebumps where they explored over your tummy.

“Tell me to stop.” His voice was low in your ear as his hand moved closer to your chest.

You stayed quiet; he ran a finger over the underside of your breast. His movements were slow, cautiously exploring your flesh. He finally reached up to cup your breast, his big hand igniting your nerves where he touched. For a moment he just held you like that, as if he was committing the feel to memory. His first squeeze was more for him than for you, but it felt damn good nonetheless. You let out a soft sigh, relishing in the feeling. He squeezed again, spurred on by your encouragement.

“What do you like?” He asked. You whispered back how you liked to be touched and he complied, rubbing and pinching at your nipples while you sighed again. You could feel him fully hard in his sweatpants behind you, the heat of his length and the teasing of your chest making you grow wet in his shorts.

“Kai,” you whined, growing impatient with his touches, wanting more. You ground your hips back against him. You could feel his cock through your shorts and it was making you desperate.

Kai stifled a groan from behind you at your neediness. His hand cautiously moved down from your breasts, pausing to squeeze the plush of your tummy as it ventured down. His fingers paused, dipping just under your waistband to gently stroke your skin there.

----

Kai gasped when he realized you weren't wearing any panties. Of course, he thought. You must've left them to dry with the rest of your clothes. He was hard before, but discovering that you were whiny and needy in his shorts without panties on made him grow impossibly harder.

He reached down, through the soft tuft of hair to find your pussy. You moaned when his fingers finally found your clit. He liked that sound, wanted to hear it again. You spread your legs a little, granting him better access to your body. He dipped his fingers through your soft folds, finding you wet for him. He couldn't help but moan as he explored your heat, coating his fingers in your wetness.

You let out a series of quiet gasps and whines as he teased you, rubbing small circles on your clit and through your folds. He found your entrance after a moment but was nervous to slip his fingers inside. Your impatient hips bucked at his hand and broke his questioning thoughts. He slowly sunk one of his slender fingers into your wet heat. You buried your face in his pillow to stifle your cry when he did. Your noises were like music to his ears and he slowly pumped the finger in and out, relishing the feeling of your walls sucking him in.

“More,” you gasped quietly, “please.”

He obliged, adding a second finger. You were keening now, rocking your hips to meet his hand as it pumped into you. The cheap bedframe squeaked softly with your movements but Kai didn't think it was anything loud enough for his roommates to hear.

You whined when he curled his fingers, throwing your head back onto his shoulder. “Kai, Kai,” you babbled, desperation dripping from your voice. You were so wet beneath his hand. “Wanna kiss you. Need to kiss you before you make me cum.”

He laughed at that. “What do you mean?” He slowed his movements when you gripped his forearm, but kept his fingers buried in your pussy.

“You're gonna make me cum, but,” your voice was shy as you continued, “I really wanna kiss you. I haven't even kissed you yet.”

Kai felt himself blush at your words. Gosh you were sweet. He smiled and kissed your cheek where he could reach from this position before removing his hand from your shorts.

You were quick to shuffle so you straddled his lap. Your clothed heat rested on his erection, which was almost painfully hard. He could just make out your features in the low light. You were so pretty, smiling down at him. He wanted to kiss you so bad. So when you leaned forward he sat up to meet you.

Your lips were soft against his, the first kiss relatively chaste as you pulled away to admire him. He basked in your gaze, loving the way you looked at him with such affection. When you kissed him again it was deeper.

----

Kai had perfect lips for kissing. He opened up to you like a flower on the second kiss. You traced his bottom lip with your tongue before he parted his lips slightly, granting you access to taste him. He moaned quietly into the kiss, hands settling around you. He brought you closer with the hand on the back of your head and gripped tightly at your ass with the hand that had been playing with your pussy just moments ago.

You shifted in his lap as his tongue explored your mouth. The change in pressure caused him to groan loudly into the quiet of his room. He broke the kiss but stayed close, whispering your name against your lips. “Please, I'm so sensitive right now.” His voice was deep and rough, held back from a full plead.

You smiled and kissed him again. “I've been teasing you for a long time haven't I?” You said, half pouting. You placed your lips right against the shell of his ear as you whispered- “you can fuck me if you want.”

His whine was stifled in his throat but you still caught it. You could feel his cock twitch beneath you at your words. Gosh, he was big. You could properly feel him now that you were straddling him. You didn't want to cum without having kissed him, but his teasing had left you needy and aching for him to fill you up again.

“Please,” was all he said before you nodded, tugging at the hem of his shirt.

“Wanna see you. Can I take this off?” He was happy to oblige, nodding before lifting his arms to let you undress him. You pulled his sweatshirt off you, letting him take in the sight of you in the dim light. The two of you sat like that for a moment, admiring each other. His hand reached out to trace over your skin once again, taking in your form in the low light. You did the same, running your fingers over his broad chest and wide shoulders. His hands continued to love on your tummy, more than anyone had done in the past. You found it cute, like most things about him, and appreciated that he seemed to enjoy a part of you you'd often been told to conceal.

Soon enough his hands found the hem of your- his- shorts again. You had to get off his lap to slide them off of you, your wetness clinging to the material as you did. Kai shucked off his bottoms as you did yours and you settled onto his lap again, the both of you fully naked in one another's embrace.

You could feel Kai's heartbeat racing under the hand you held to his chest. “Are you excited?” You teased.

“Y/n,” he started, “I really like you. I've liked you for a long time now. Since I first met you, I've liked you.”

You squeezed his hand, wanting to reassure him that you felt the same. “I really like you too, Kai. For a while now too.” He kissed you again. The kiss was charged with emotion, he poured his feelings into it and you reciprocated.

When the kiss broke you were both breathing hard. “You have a condom, right?” He nodded quickly, reaching to throw open the top drawer of his bedside table. Inside was a full box of unopened foils.

Sliding the condom onto Kai's length made your pussy clench around nothing. He was so big and heavy in your hand. He gasped like it hurt when you first held his cock, his angry tip a leaking mess of precum. He watched you with huge eyes as you rolled it on.

You spit onto your hand, slicking him up through the thin barrier. He couldn't stop the whine that he emitted as you stroked him.

When you finally hovered over his lap again you felt dizzy with anticipation. Kai's fingers had been long and stuffed you full, but his cock was surely going to fill you to the brim. You lined him up at your entrance and began to sink down.

His mouth fell slack when his fat tip pushed past your tight entrance. You took him inch by inch, fighting the urge to just sit on it, forcing yourself to take it slow and adjust. It felt like he was splitting you open. He was bigger than anyone you'd had before. Long and thick, he hit every spot inside of you as you finally rested on his hips, taking him to the hilt. You had to catch your breath.

----

Kai’s eyes were squeezed tight, his breaths heavy. The feeling of being inside of you better than he had imagined. You were so warm, your wet walls holding him so tight even through the latex barrier.

“Kai,” you whispered, rubbing his arm to bring him back to you. “Is this still okay?”

He opened his eyes and nodded. “Yes, yes. Just need a sec.” He was trying his hardest not to cum right there. But you were so beautiful in the shifting hues coming from his pc, the dim light illuminating your features. The moonlight from the crack in the blinds shone on your lashes as you watched him carefully.

“Okay,” he finally said, feeling like he wasn’t about to immediately cum at the slightest sensation. “I’m ready.”

You hummed and kissed him again before leaning back and slowly rolling your hips. His hands flew to your thighs, gripping them tightly as he tried to keep from moaning loudly and alerting his roommates to what was happening. You smiled down at him, speeding up a bit.

He was mesmerized by the way you looked as you rode him. He must’ve looked like a dumbstruck fool the way you giggled at his expression. “You like what you see?”

“Very much. You’re so beautiful.” Your face split into a huge smile and you kissed him again.

“I think you’re pretty beautiful too.” Kai felt himself blush at your words, not used to praise like this.

He wasn’t going to last very long, not with your sweet words and the slow drag of your walls around his cock. He moved his hands from where they rested, exploring the curves of your body, committing them to memory. He’d always had a thing for soft tummies, but your thick thighs, full breasts and even the soft creases of your back all delighted him. His touches spurred you on, your increased enthusiasm pushing him closer to the edge.

“Gonna cum.” He whined.

“Touch me here,” you guided his hand to your clit. “We’ll cum together.”

He fought through the building pressure, gathering your wetness to coat his thumb. A sigh escaped your lips when he rubbed your clit. He easily matched the pace you set with your hip, musician’s muscle memory kicking in.

“I’m so close,” his voice was strained, “gonna-”

His orgasm hit him hard. His hands squeezed hard at your hips as you rode him through his high, chasing after yours. The sounds you made when you came were music, a falling set of whimpers and stutters that washed over Kai like a wave. You slumped into Kai’s chest, aftershocks still causing your pussy to flutter and clench around him. He wrapped his arms around you, holding you in a sweet embrace as you both came down from your highs.

----

You hummed contentedly into the space between Kai’s shoulder and throat. He was warm and strong and all around you. You felt safe and cozy in his arms and completely blissed out from his cock. You knew you needed to clean up but you wanted to savor this moment for as long as you could.

“Hey,” Kai’s voice was a soft whisper above you. You hummed again in acknowledgement. “Do you think maybe we could go on a date sometime?”

You laughed, burying your face into his chest. Gosh, this boy. You propped yourself up onto your elbow, taking in the beauty of Kai’s features as he looked at you expectantly. “I would love that.” His smile was immediate. “And by the way, you could have asked me at any point in the year and I would’ve said yes.”

You couldn’t quite make out the blush that spread across his cheeks in the low light, but you kissed him again to let him know you meant it. You settled back onto his chest and he placed a soft kiss to the top of your head. “I’m kind of glad I left my bag in that office now.”

You could feel Kai’s laugh through his chest. “I am too.”