5

Later that night, the house had settled into quiet. Jake and Sarah had disappeared into the living room to watch a movie, their laughter drifting faintly down the hall. Mia waited in her room until she heard Sarah’s voice outside Ethan’s door.

“He’s in there catching up on some reading,” Sarah had said with a casual wave. “Good luck if you need anything—he’s probably half-asleep already.”

Perfect.

Mia’s heart beat a steady, excited rhythm as she picked up her biology textbook—the thick one from her first-year course that covered advanced human physiology, including the reproductive system chapter she had deliberately dog-eared. 

She wore a soft, oversized college hoodie that belonged to Jake but hung loose on her frame, the hem brushing mid-thigh. Underneath, only a pair of tiny cotton panties. No bra. Her nipples already peaked against the fabric from anticipation. 

She had brushed her hair until it fell in soft waves and dabbed a touch of vanilla scent on her wrists and the hollow of her throat.

This was the moment to test how far the crack in Ethan’s restraint had spread.

She padded barefoot down the hallway and knocked lightly on his door.

“Come in.”

Ethan sat on the edge of his bed in a plain black t-shirt and basketball shorts, laptop open beside him. The guest room felt familiar—posters from their high school days still on the walls, his duffel bag half-unpacked in the corner. He looked up, surprise flickering across his face when he saw her.

“Hey, squirt. What’s up?”

Mia stepped inside and closed the door behind her with a soft click, holding the textbook against her chest so it pressed her breasts together just enough to create a subtle swell at the neckline of the hoodie. 

“Sarah said you were in here. I… I need help with something from bio. We’re on the reproductive system chapter, and I don’t get a few parts. You’re really good at biology, right? And basketball, but that’s not helping tonight.”

Ethan’s eyes flicked to the book, then back to her face. He rubbed the back of his neck. “Uh, yeah… I took the advanced version last year. What part’s giving you trouble?”

Mia moved closer, sitting on the bed beside him—not too close, but near enough that her bare thigh brushed his knee when she opened the textbook across both their laps. 

The page showed detailed diagrams of male and female reproductive anatomy, labels for arousal, erection, lubrication, orgasm. She pointed to a section on the physiological response during sexual stimulation.

“This part,” she said softly, voice innocent. “It talks about how blood flow increases, how tissues swell… I keep mixing up the mechanisms. Can you explain it like I’m brand new?”

Ethan cleared his throat. His gaze dropped to the page, then involuntarily to the way the hoodie had shifted, revealing the smooth skin of her upper thigh and the faint outline of her hard nipples through the fabric. He focused hard on the diagram.

“Okay… so, basically, during arousal, the parasympathetic nervous system triggers vasodilation. More blood rushes in, causing erection in guys or engorgement and lubrication in girls. It’s all about preparing the body for… uh… penetration and climax.”

Mia leaned in a little, her shoulder pressing lightly against his arm. Her scent—vanilla and warm skin—drifted toward him. “Like this?” She traced a finger along the diagram of the clitoris and labia, circling slowly. “It says the clitoris has thousands of nerve endings. Does that mean even light touch can cause… intense reactions?”

Ethan’s jaw flexed. He shifted on the bed, trying to create space, but the textbook kept them tethered. His shorts suddenly felt tighter. “Yeah. Super sensitive. The whole area gets swollen and wet to reduce friction.”

Mia nodded, biting her lower lip in concentration. She turned the page to the male anatomy section, her knee now resting against his thigh. “And for guys… the penis fills with blood, gets hard. What if someone’s trying really hard not to react? Does the body just… ignore what the brain wants?”

Her voice stayed light, curious, like any student asking for help. But her free hand rested on the bed between them, fingers inches from his leg. She shifted again, the hoodie riding higher so the hem barely covered the edge of her panties.

Ethan’s breathing had grown deeper. A visible bulge was forming in his basketball shorts; he crossed one leg casually over the other, but it only drew more attention. “The body doesn’t always listen to the brain, squirt. Especially if the stimulus is… strong.”

Mia looked up at him through her lashes, eyes wide and guileless. “So if I touched someone who was trying to stay calm, it might still… wake up?” She let her fingertips graze his knee, innocent as a question mark, then drew a small circle there.

Ethan inhaled sharply. Heat flooded his face. His cock throbbed fully now, straining against the thin fabric, the outline clear if she glanced down. “Mia…” He started to pull back, but the textbook pinned him. “We should focus on the material.”

She smiled softly, turning another page. “Okay. One more thing—this part about orgasm. It says muscle contractions happen involuntarily. Like, once it starts, you can’t really stop it?” Her thigh pressed more firmly against his now, warm and bare. The hoodie slipped off one shoulder, exposing the freckled curve of her breast and the tight peak of her nipple.

Ethan’s hand fisted the sheet beside him. Sweat beaded at his temple. His mind screamed bro code, girlfriend, Jake’s sister, but his body betrayed him—cock rock-hard, pulse hammering in his ears. 

The images from yesterday flooded back: her in that bikini, water droplets tracing her freckles, ass barely covered. Now she sat here in his room, asking about sex in that sweet voice while her body radiated heat.

“Yeah,” he managed, voice rough. “Once the threshold is crossed… it’s pretty much unstoppable.”

Mia closed the book slowly, letting it rest on his lap—right over the prominent bulge. The weight pressed down on his erection for a second before she lifted it away. She stood, tugging the hoodie back into place with an innocent tug.

“Thanks, Ethan. That actually helped a lot. I think I get it now.”

She walked to the door, then paused, glancing back over her shoulder. Her eyes dropped briefly to the obvious tent in his shorts before meeting his gaze again. A small, satisfied grin curved her lips—private, knowing, victorious.

“Goodnight… squirt’s tutor,” she whispered playfully, then slipped out, closing the door behind her with a quiet click.

Ethan sat frozen on the bed, chest heaving, cock throbbing painfully against the fabric. He dragged both hands down his face, muttering a string of curses under his breath.

The mantra was getting harder to believe.