Archive of Our Own ^beta

“Senku-chan, what are you still doing up~?” Gen said as he moved the curtains of the science lab aside and stepped in.

“Finishing up packing for the departure to the US,” Senku replied, annoyance lacing his voice. He loved his boyfriend truly (though he’d never admit it), but it was getting harder to finish anything without the night ending in them making out.

“I thought you did that yesterday,” Gen questioned.

“Yeah, until you decided to shove your hands under my clothes,” Senku said with an eye roll.

“Yeah, but—” Gen leaned closer, brushing his lips against Senku’s ear. “You loved it.”

His hand slithered under Senku’s tunic, but Senku caught his wrist before it reached his nipple.

“If you’re horny, you’re gonna behave and wait till I finish this,” Senku said flatly. He glanced at Gen’s pouting face.

Gen pulled away, muttering, “Ean-may…” as he sat down with a sulky frown.

Senku smirked. “Good boy~,” he said in a low, sultry voice.

A blush crept up Gen’s cheeks. Let’s see how long he stays like that, Senku thought.

As he packed away the last of his supplies, Senku felt Gen’s gaze burning into his back. Every time he reached up for something or bent down, Gen’s eyes followed. By the time he finished, Gen crept up behind him and wrapped his arms around Senku’s waist.

“Let’s get to the fun part~,” Gen teased.

-^-

When they reached the observatory, Gen practically tackled Senku to the floor. Their lips crashed together in a rough kiss, teeth clashing, hands roaming. Gen yelped as Senku flipped them over.

“You’re not fucking me till you’re bruised, good mentalist,” Senku smirked, pinning Gen’s wrists with one hand. With the other, he tugged at the rope keeping Gen’s obi and yukata together. He deepened the kiss as the strings came loose, peeling away fabric until Gen’s pale skin was exposed, glowing in the moonlight.

“Fuck, staying still for me, Gen. You really want this, don’t you?” Senku murmured, smirking.

Gen arched beneath him, desperate. “Always, darling.”

Senku kissed his neck, leaving a trail of purple bruises as Gen moaned and gasped. He moved lower, biting at Gen’s chest and sucking his nipples until Gen’s whimpers grew louder. Slowly, he worked down his torso, admiring the collection of bruises he’d left behind.

“God, mentalist, you don’t know how hot you look right now,” Senku muttered, barely holding back a groan.

Gen shoved him off suddenly, breaking free from his grip. “Patience isn’t something I have today, Senku.”

He quickly undressed Senku, stripping him down until only underwear remained. Then, with one final tug, Senku was bare beneath him. Gen’s breath hitched as he admired the view, reaching for a vial hidden in his overcoat pocket. Senku stopped his hand, intertwining their fingers. Their faces were inches apart.

“Well, fucking me is gonna have to wait,” Senku said, hooking a finger on Gen’s waistband.

“I thought you didn’t like giving head, dear Senku?” Gen smirked as he slid his own clothes off.

Senku’s pupils were blown wide. He pushed Gen down and spread his legs, teasing kisses and bites along his inner thigh until Gen was moaning freely. His hand wrapped around Gen’s length, stroking slowly before licking from base to tip. Then, with deliberate control, he took him into his mouth, bobbing his head as Gen’s moans grew louder.

Gen’s hand tangled in Senku’s wild hair, helping guide the pace. He pulled Senku off before climax could take him. “You don’t want me cumming till the good part, do you, dear Senku?”

Senku only looked up through his lashes, lips wet, expression sinful.

They shifted positions, Senku lying beneath Gen now. Gen slicked his fingers with oil, pressing gently against Senku’s entrance.

“You ready, dear?”

“Yes, mentalist, you can prep me,” Senku huffed, rolling his eyes at the teasing.

One by one, Gen stretched him open, curling his fingers until he found the spot that made Senku cry out. Senku’s back arched as his moans filled the observatory. When Gen finally pulled his fingers away, Senku gasped at the emptiness.

Gen lined himself up and kissed Senku’s cheek. “You ready?”

“Yes, mentalist. Now stop wasting time and fu—” Senku’s words were cut short with a loud gasp as Gen pushed halfway in.

“Fuck, warn me before you do that,” Senku hissed.

“Sorry, dear Senku, but I’m impatient. Besides, you sound so sweet when I pound you senseless.”

He pushed in to the hilt, both of them moaning. Senku wrapped his arms around Gen’s neck, legs locked around his waist.

“If you don’t move, I’ll finish myself, mentalist,” Senku muttered.

Gen chuckled, kissing his cheek as he began thrusting. Soon the pace was relentless, their cries echoing in the night. Gen adjusted Senku’s leg over his shoulder, hitting that perfect spot again and again until Senku was a moaning mess beneath him.

“Does it feel good, Senku?” Gen growled. “Does it feel good when I fuck you to a moaning mess?”

Senku could barely form words. “Fuck~ right there, don’t stop, Gen!”

Their rhythm grew more frantic as both approached release. Senku tugged hard on Gen’s hair, body trembling.

“Gen… I’m… close,” he gasped.

“Me too, baby. Oh fuck, can I come inside you? Please?” Gen begged.

“Please do, fill me up,” Senku pleaded back.

That was all it took. They came together with cries of pleasure, Senku’s release painting his chest while Gen filled him deep inside.

Afterward, both lay panting, sweat-drenched and trembling. Gen pulled out slowly, cleaning Senku with a damp cloth before curling against him.

“So, how was that?” Gen smirked.

“Good… I hope I can walk tomorrow,” Senku chuckled.

Gen tackled him with a kiss. “Good, because if you didn’t like it, I’d have fucked you again.”

“You tell me that now? You’re a brat, mentalist.”

“Oh~ so it was really good?” Gen teased, propping his head on his hand.

Senku’s face flushed crimson, and he turned away. “Whatever, mentalist. Go to sleep.”

Gen pulled a blanket over them, spooning Senku as he whispered softly, “Goodnight, dear Senku.”