1

The jealousy hit Mia like a slap of summer lightning sharp, electric, and impossible to ignore.

Mia had just turned 18 two weeks ago, and the summer heat in their quiet suburban neighborhood felt thicker than ever. Her older brother, Jake, was home from college for the break, and as usual, his best friend Ethan was practically living at their house. 

Ethan was 22, tall, with messy dark hair, broad shoulders from years of basketball, and that easy, cocky grin that made Mia’s stomach flip every time he looked her way.

She’d had a crush on him since she was 14, but now… now she was legal, and the way his eyes lingered on her when Jake wasn’t looking had changed everything.

She stood frozen at her bedroom window, her fingers gripping the sill so tightly her knuckles bleached white. Down by the pool, the afternoon sun turned everything golden and cruel. Jake was laughing loudly, his hands already wandering over some college girl in a bright red bikini. But it wasn’t Jake who made Mia’s stomach twist into knots.

It was Ethan.

Ethan had his girlfriend—Sarah— pinned against the pool’s edge. He was kissing her deep and slow, one hand cupping the back of her neck while the other rested possessively on her hip. Sarah sighed into his mouth, arching against him like she belonged there. Like she had every right to his attention.

Mia’s chest burned. She was eighteen now. She was longer the annoying little tag-along who used to beg them to let her play video games. Their parents were gone for two full weeks to Europe on some fancy anniversary trip and Jake was supposed to be “babysitting” her. The house, the pool, the entire lazy summer afternoon should have been hers to finally do something with.

She had planned it so carefully. Slipped into her skimpiest white sundress, the one that barely skimmed her thighs and showed the soft swell of her breasts when she moved just right. She had spent an hour curling her long dark hair, glossing her lips, even spritzing perfume in all the secret places. Today was supposed to be the day Ethan finally looked at her differently.

Instead, he was kissing someone else.

Mia’s jaw tightened. Fine. If he wanted to pretend she was still just Jake’s harmless little sister, she would make it impossible for him to keep pretending.

She stepped back from the window, heart racing. In one quick motion she peeled the sundress over her head and let it puddle on the floor. Her reflection stared back from the mirror—smooth skin flushed with heat, perky breasts with nipples already tight from nerves, a narrow waist flaring into hips she knew looked good when she walked. She opened her drawer and pulled out the tiniest black bikini she owned. The one she had bought on impulse last month and never dared wear.

The top was little more than two tiny triangles held together by thin strings. The bottoms were even worse—a thong cut that disappeared between her rounded ass cheeks, the front a narrow V that would ride high on her hips. 

She tied the strings carefully, adjusting the triangles so they barely covered her nipples, then turned to check the back. The strings sat high on her hips, framing the smooth curves of her ass perfectly.

She looked dangerous. Soft. Tempting and exactly what she needed. Mia took a slow breath, lifted her chin, and headed downstairs.

The moment she stepped onto the sun-warmed patio, the heat wrapped around her bare skin like a caress. Jake noticed first.

“Jesus Christ, Mia,” he groaned, shielding his eyes. “What the hell is that? Go put on real clothes.”

His date giggled, but Mia only smiled sweetly, twirling once so the tiny skirt of strings swayed. “It’s hot out, Jake. Relax.”

Her eyes found Ethan.

He had pulled back from his girlfriend when he heard Jake’s voice. His gaze snapped to Mia and stayed there. Those familiar dark eyes—eyes that had teased her for years—dragged slowly down her body: over the barely-there top clinging to her breasts, the flat plane of her stomach, the scandalously small bottoms that left her long legs and the curve of her ass on full display. His lips parted slightly. His girlfriend was still talking to him, but he didn’t seem to hear.

Mia felt a thrill shoot through her. She pretended not to notice, walking toward the pool with a gentle sway in her hips, the concrete warm under her bare feet.

“Hi, Ethan,” she said softly, stopping at the edge just a few feet from him. Water droplets glistened on his chest and abs. His swim trunks clung to powerful thighs. “Mind if I join you guys?”

His girlfriend turned, eyes narrowing slightly. Ethan cleared his throat.

“Sure, little sister,” he said, voice a little rougher than usual. “Pool’s big enough.”

Little sister. The words sent a spark of irritation through her, but she smiled anyway, sweet and innocent. She turned slowly, giving everyone—especially Ethan—a perfect view of her ass as the thin black strings disappeared between her cheeks. Then she dove into the deep end in one graceful arc.

The cool water swallowed her. When she surfaced, she was closer to Ethan than she had planned, treading water smoothly. Her bikini top had shifted just a little; one edge of the triangle had slipped, revealing the soft inner curve of her breast and the hint of a pink nipple. She made no move to fix it right away.

Ethan’s eyes flicked down, then quickly back up to her face. His jaw flexed.

“New swimsuit?” he asked, trying for casual.

Mia tilted her head, water streaming down her neck and between her breasts. “Yeah. Thought it was time to try something different. Do you like it?”

His girlfriend splashed water at him playfully, but Ethan barely reacted. His gaze lingered on Mia a second longer than it should have.

“It’s… small,” he said finally. “You sure your brother’s okay with that?”

Jake snorted from the other side of the pool. “I’m not okay with it, but she never listens.”

Mia laughed lightly, the sound bright and teasing. She swam a little closer to Ethan, close enough that her knee brushed his thigh under the water for the briefest moment. “I’m eighteen, Ethan. I can wear what I want. Besides… it’s just us here.”

She let her fingers trail along the surface of the water, drawing lazy circles. Droplets clung to her lashes. She looked up at him through them, lips parted just slightly, the picture of innocent temptation.

Ethan’s eyes darkened. He glanced once at his girlfriend, who was now chatting with Jake’s date, then back at Mia.

“You’re still my little sister, Mia,” he murmured, low enough that only she could hear. “Even if you’re all grown up now.”

The words should have annoyed her. Instead, they sent heat curling low in her belly. She moved a fraction closer, her breasts nearly brushing his chest under the water. The thin fabric of her bikini top was almost translucent when wet; she knew he could see the hard points of her nipples pressing against it.

“Maybe I don’t want to be just your little sister anymore,” she whispered, so softly it could have been the breeze. She let her foot graze his calf under the water—accidental, teasing—before pulling back with a shy smile. “But I guess old habits die hard.”

Ethan’s hand twitched at his side, like he wanted to reach for her but stopped himself. His breathing had changed, just a little deeper. His girlfriend called his name, and he answered distractedly, never fully looking away from Mia.

She turned then, swimming toward the shallow end with slow, deliberate strokes, letting him watch the way her body moved through the water. When she reached the steps, she rose slowly, water cascading down her skin. The bikini bottoms had ridden up even higher; the thin fabric clung to every curve, outlining the soft lips of her pussy. She bent over slightly to adjust the towel on the lounge chair, giving Ethan a long, unobstructed view of her ass.

She could feel his stare burning into her.

Jake and the girls headed inside for more drinks, their laughter fading through the sliding door. For a moment, the backyard was quiet except for the gentle lap of water and the pounding of Mia’s heart.

Ethan stayed in the pool. He swam toward the shallow end, stopping a few feet away from where she stood. Water streamed down his muscled torso. His eyes traced her body again—slow, deliberate—before meeting hers.

“What you are doing is dangerous, little sister,” he said quietly, voice thick.

Mia tilted her head, innocent as ever, even as her pulse raced. She ran her hands down her wet hair, pushing it back so her breasts lifted slightly. “I’m just swimming, Ethan. What’s so dangerous about that?”

He didn’t answer right away. His gaze dropped to her chest, to the way her nipples strained against the tiny wet triangles, then lower to the soaked fabric between her thighs.

The sliding glass door rattled—Jake and the others were coming back.

Ethan’s eyes snapped back to hers, dark and stormy 

with something new. Something hungry. He turned and swam away just as Jake stepped outside with a tray of drinks.

Mia stayed where she was, heart hammering, skin tingling where his gaze had been. She had finally cracked the surface of his obliviousness.

And as Ethan climbed out of the pool, water streaming down his body, the front of his trunks noticeably tighter than before, she knew the real game had only just begun.

She smiled to herself. Let him call her little sister for now. She had two whole weeks to make him forget the word entirely.